channel responses to declining flow on the rio grande between ft quitman and presidio texas abstract a profound decline in the discharge of the upper rio grande following upstream water development set in motion a chain of responses in channel geometry and sediment budget the case of the rio grande provides a well documented example of the evolution of channel geometry in response to change in a single external variable in a regime of declining flow channel change was driven by an excess of sediment relative to the energy available to do work in the stream channel several different responses can be identified which operated at different rates responses can be ranked according to reaction time to define 3 stages in channel evolution stage i is identified as the shrinking of the channel as excess sediment was deposited within it during stage ii channel capacity began to stabilize as overbank flow carried sediment onto natural levees and floodplain valley wide aggradation began and avulsive migration resumed especially at the mouths of tributaries where stage iii is occurring lag deposits of bedload at tributary mouths are locally regrading the valley initial shrinking of the channel produced positive feedback to the decrease in discharge and sediment transport capacity not until later stages did subordinate responses appear which tended to balance the sediment budget and these involved lateral migration the river approached a balanced sediment budget both by increasing its capacity by shortening and steepening and by decreasing sediment inout by migrating away from tributaries

channel adjustments following two dam removals in wisconsin 1 we examined channel response following the removal of low head dams on two lowgradient fine to coarse grained rivers in southern wisconsin following removal channels eroded large quantities of fine sediment resulting in deposition 3 5 km downstream at one site baraboo river upstream changes were rapid and included bed degradation minimal bank erosion and sediment deposition on channel margins and new floodplain sand was transported through the former impoundment and temporarily deposited downstream at the second site koshkonong river head cut migration governed channel adjustments a deep narrow channel formed downstream of the headcut with negligible changes upstream of the head cut fluvial changes were summarized in a conceptual channel evolution model that highlighted 1 similarities between adjustments associated with dam removal and other events that lower channel base level and 2 the role of reservoir sediment characteristics particle size cohesion in controlling the rates and mechanisms of sediment movement and channel adjustment index terms 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 1857 hydrology reservoirs surface keywords dams dam removal channel evolution model

geothermobarometry in albite garnet orthogneisses a case study from the gran paradiso nappe western alps abstract the aim of this paper is to estimate syntectonic p t conditions within albite and garnet bearing orthogneisses these rocks are generally characterized by the assemblage quartz albite biotite phengite cafe garnet epidote titanite garnet contains up to 55 mole per cent of grossular k feldspar is a relict magmatic phase p t conditions are estimated using several independent methods first it is shown that exchange reactions based on the fe mg partitioning between garnet and biotite or garnet and phengite cannot be used to estimate temperatures in these rocks due to the high grossular content of garnet second maximum and minimum pressures are constrained respectively by the occurrence of albite instead of jadeite quartz and by the assemblage phengite biotite quartz third phase equilibria in albite and garnet bearing metagranites are modelled in the system k 2 o cao feo al 2 o 3 sio 2 h 2 o equilibrium curves are calculated for the observed phase compositions uncertainties in p t estimates mainly result from the choice of appropriate non ideal solution models for the garnet an application is developed for granites from the gran paradiso nappe western alps these granites show an heterogeneous deformation of alpine age expressed by mylonitic shear zones cutting across weakly deformed domains estimated p t conditions for the synkinematic assemblages are 10 16 kbar at 550 50 c

man s influence on the erosion and transport of sediment by asian rivers the yellow river huanghe example during the holocene sediment input from the yellow river to the yellow sea and adjacent areas has amounted to about 3000 km 3 detailed records from river gauging stations over the past 70 yrs together with estimates based on earlier historic records suggest that the river has contributed 2300 km 3 of sediment during the last 2300 yrs an average discharge of 1 km 3 yr 1 x 10 9 t yr prior to extensive agricultural use of the loess plateau in northern china beginning about 200 bc therefore the river s load must have been about 0 1 km 3 yr an order of magnitude lower than that at present a broad delta 20 m below sea level suggests that early holocene rates were higher than the pre agricultural average and therefore that middle holocene loads were low

nature of the elzevir mazinaw domain boundary grenville orogen ontario the mooroton shear zone msz of the metasedimentary belt of the grenville orogen in ontario separates the mazinaw domain to the east from the elzevir domain the shear zone is composed of mafic metavolcanic metaclastic and marble mylonites and is characterized by a subvertical foliation which crosscuts the regional foliation and a near vertical stretching lineation microstructures indicate deformation occurred under crystal plastic conditions and shear sense indicators give movement of east mazinaw side up the geometry of the msz which follows the eastern margin of the elzevir tonalite implies that lithologic anisotropy guided its location garnet biotite and garnet hornblende peak temperatures are juxtaposed across the msz with temperatures ranging from 460 to 530 c in the southeastern elzevir and 490 to 620 c in the southwestern mazinaw conditions in amphibolite facies limiting barometers applied to rocks in both domains show no significant offset petrologic data within the shear zone

young high temperature granulites from the base of the crust in central mexico characterization of the lower continental crust is essential to understanding processes of crustal formation and evolution many workers have concluded that the lower crust is composed of granulite facies rocks see for example refs 1 2 but many exposed granulite facies terranes seem to have mid crustal rather than lower crustal origins3 5 here we present new data from direct samples of the lower continental crust in the form of metapelitic rock fragments brought to the surface by quaternary volcanism in central mexico these xenoliths contain exsolved ternary feldspars that record extremely high minimum metamorphic temperatures of 950 1 100 c the highest yet known to be preserved in deep seated metamorphic rocks the metamorphism seems to be the result of underplating by basaltic magma and to be regional in extent our barometry on these samples demonstrates that granulite facies metamorphic rocks are present in the lower crust and provides important constraints on tectonic models and interpretations of geophysical data chemical and text lira i evidence suggest that the xenoliths were not able to cool to below 850 900 c before being entrained in their host magmas indicating that the granulite facies metamorphism occurred no more than 30 myr ago

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

the effect of the coarse aeolian sand on siltation of the inner mongolian reach of the yellow river the yellow river flows through an extensive aeolian inner mongolian plateau with a total length of 673 km owing to the high erodibility of the wulanbuhe and kubuqi deserts and the impacts of its upstream reservoirs the siltation of the inner mongolian reach of the yellow river is caused essentially by the aeolian particles larger than 0 1 mm which are very different from the sediment 0 05 mm of the lower yellow river coming from the loess plateau during the period 1954 2000 the total accumulated sediment of this area was about 20 1 108 t the coarse sediment larger than 0 1 mm as about 15 2 108 t and the fine sediment less than 0 1 mm fs about 4 9 108 t in particular there was 6 1 108 t as coming from the wulanbuhe desert and 5 82 108 t as from the kubuqi desert deposited in the river channel of the inner mongolian reach representing 78 6 of the total coarse sediment larger than 0 1 mm

channel bed adjustments following major aggradation in a steep headwater setting findings from oyabu creek kyushu japan abstract a typhoon in 1993 induced major aggradation along oyabu creek a steep gravel bed mountain stream in kyushu japan processes of sediment reworking are inferred from a 7 year monitoring program that measured adjustments to channel cross sections the longitudinal profile and the extent distribution of bedrock outcrops along a 3 km study reach over time the reach adopted a riffle and pool structure with notable increase in the area of exposed bedrock on the bed this adjustment process was characterised by progressive reduction in sediment storage change per unit flow the relaxation pathway following disturbance induced by the typhoon was shaped by the magnitude and frequency of subsequent rainfall events the capacity of these events to transport available sediments and physical linkages between reaches adjacent subreaches demonstrated differing relaxation pathways in response to these influences induced by spatial and temporal variability in threshold conditions along the channel longer term evidence indicates that responses to major disturbance such as the 1993 typhoon occur as cycles of around 20 year duration a relaxation period of 7 years is required to attain a quasi equilibrium bed configuration and rate of sediment flux the timeframe of cycles is considered to reflect changes to hillslope channel bed coupling marking the period required to generate sufficient sediment stores to reactivate phases of aggradation and subsequent degradation

long term morphodynamic changes of a desert reach of the yellow river following upstream large reservoirs operation abstract china s yellow river has experienced its dramatically decreasing trend for the flow discharge since the construction and operation of large reservoirs located upstream this low flow regulation has triggered a severe aggradation of the ulan buh desert channel of the yellow river because the declining flow exhibits no capability to scour and carry away large amount input of desert sands from the ulan buh desert twenty monitoring cross sections documented the ulan buh desert channel has experienced its increasing aggradational trend in conjunction with its lateral migration decreasing trend from 1966 to 2005 which is opposite to the normal pattern of aggradation with deepening or symmetrical infilling for a channel located downstream of a reservoir the channel aggradation can also be identified two stages slow aggradation and rapid aggradation slow aggradation is characterized by the channel bed elevation rising 9 5 cm on average between 1968 and 1985 which responded to the operation of the liujiaxia reservoir during this period the flow discharge was similar to pre dam flow conditions but the sediment transport reduced to half of its pre dam value because of about 0 24 108 t of desert sands entering the channel from the ulan buh desert annually this dilute flow indicated not to scour the channel as expected but contrarily to cause the channel aggraded rapid aggradation followed completion of the longyangxia reservoir with the channel bed elevation rising by 73 cm on average between 1986 and 2005 in this period the combined regulation of liujiaxia and longyangxia reservoirs has caused the flow discharge decreasing dramatically which is more beneficial for accumulation of the desert sands 0 19 108 t yr 1 on average in the desert channel and led to the channel aggradation rate accelerated rapidly

how to resolve the controls on mesothermal vein systems in a goldfield characterized by sparse kinematic information and fault reactivation a structural and graphical approach current mine exposures of auriferous veins in the charters towers goldfield ctgf are characterized by a scarcity of kinematic indicators furthermore the dip direction of exposed and historically mined orebodies largely coincides with the orientation of pre existing discontinuities consequently the reactivation of earlier structures during gold deposition is strongly indicated both factors complicate the structural analysis of the auriferous vein systems as slip on earlier faults likely occurred before new rock failure and evolution of fault networks reflecting the stress field present at the time of gold deposition despite access to drillcore open pits and underground workings extracted data were limited to ten occurrences of wear groove striations and three reverse separations of dykes and a pegmatite cut by sulphide bearing quartz veins because of the scarcity of kinematic information the structural analysis focused on the geometry of veins and ore shoots also applying basic graphical and kinematic methods

changes in river regime after the construction of upstream reservoirs this article presents and analyses many years of investigations in china on the fluvial processes downstream of impounding and detention reservoirs the study covers the change in hydrograph the recovering of sediment concentration along the river course the degradation of stream bed the adjustment of longitudinal profile the coarsening of bed material the change in channel width and the trend of channel pattern variation for alluvial streams downstream of impounding reservoirs without confluence of major tributaries the degradation may extend to a great distance below the dam in the process of reducing the sediment carrying capacity of the flow to match the diminished sediment supply the coarsening of bed material is a factor of equal if not greater importance as compared with the flattening of channel gradient in places where the flow has not been sufficiently cut down and the bank is erosive non resistant a receding of banklines may take place in concurrence with the deepening of the river bed below detention reservoirs even if the total runoff and sediment supply remain essentially unchanged the modification of the hydrograph is sufficient to enhance the deterioration of the downstream channel

calculation of co 2 activities using scapolite equilibria constraints on the presence and composition of a fluid phase during high grade metamorphism thermodynamic and phase equilibrium data for scapolite have been used to calculate co2 activities aco2 and to evaluate the presence or absence of a fluid phase in high grade scapolite bearing meta anorthosite granulites calc silicates and mafix xenoliths the assemblage scapolite plagioclase garnet quartz may be used to calculate or limit aco2 by the reaction meionite quartz grossular anorthite co2 granulites from four high grade terranes grenville province canada sargut belt india furua complex tanzania bergen arcs norway yield aco2 0 4 1 with most 0 7 for scapolite bearing granulites from the furua complex in which aco2 0 9 calculated h2o activities ah2o based on phlogopite dehydration equilibria are uniformly low 0 1 0 2 the aco2 calculated for meta anorthosite from the grenville province ontario ranges from 0 2 to 0 8 for grenville meta anorthosite also containing epidote the ah2o calculated from clinozoisite dehydration ranges from 0 2 to 0 6 calc silicates from the grenville sargur and furua terranes mostly yield aco2 1 the calculated fluid activities are consistent with metamorphism 1 in the presence of a mixed co2 h2o fluid phase in which co2 is the dominant fluid species but other c o h s species are minor 2 in the absence of a bulk fluid phase fluid absent metamorphism or 3 in the presence of a fluid bearing melt phase the results for many granulites and grenville meta anorthosite are consistent with the presence of a co2 rich mixed co2 h2o fluid phase in contrast the relatively restricted and low values of aco2 for calc silicates require an h2o rich fluid or absence of a fluid phase during metamorphism the range of values for xenoliths are most consistent with absence of a fluid phase the primary implication of these results is that a co2 rich fluid accounts for the reduced ah2o in scapolite bearing granulites however scapolite may be stable with a wide range of fluid compositions or in the absence of a fluid phase and the presence of scapolite is not a priori evidence of a co2 rich fluid phase in addition close association of scapolite free mafic granulites with scapolite bearing granulites having identical mineral compositions in the furua complex and the absence of scapolite from most granulite terranes implies that a co2 rich fluid phase is not pervasive on an outcrop scale or common to all granulite terranes

compatibility of geobarometers in the system cao feo al_ 2 o_ 3 sio_ 2 tio_ 2 cfast implications for garnet mixing models in the system cao feo al 2 o 3 sio 2 tio 2 several barometers have been experimentally calibrated hese include alm 3 ru 3 jim sil qtz grail 2 alm gr 6 ru 6 ilm 3 an 3 qtz grips 2 alm gr 3 fa 3 an fag 3 an gr 2 ky qtz gasp 2 fs fa qtz ffq and gr qtz an 2 wo wags because grips grail and gasp form a linearly dependent set they provide a stringent test for the accuracy of a x models for grossular almandine solid solutions the ganguly and saxena garnet solution model yields a calculated position for gasp two kb above a best fit to the available experimental reversals using these reactions to constrain mixing parameters for grossular almandine garnets on a ca fe 2 1 cation basis yields w h cafe 6240 j w h fcca 23800 j and w s cafe w s feca 11 4 j k model 1 or w h cafe 628 j wh feca 17080 j model 2 using the measured pyrope grossular value for w s 6 216 j k grips can be further

the grenville front south of val d or quebec abstract the tectonometamorphic history of rock assemblages is unravelled throughout a 50 30 km strip across the grenville front the boundary between the superior and the grenville provinces in the canadian shield this was accomplished by applying geothermobarometric techniques to zoned garnets systematic analysis of garnetiferous assemblages revealed that 1 1 primary garnet grti cores grew during a high t low p metamorphic episode and 2 2 secondary garnet grtii cores as well as most of the grti rims grew during a low low t high p metamorphic episode the two sets of p t conditions can by comparison with available geochronological data be assigned to the kenoran late archaean and grenvillian mid proterozoic orogenies respectively a prominent ductile shear zone traverses the 50 30 km strip and divides the area southeast of the grenville front into two regions with contrasted tectonometamorphic behaviour the eastern region is composed of migmatitic and charnockitic gneisses representing intermediate to lower levels of the archaean crust the western region is composed of migmatitic metasediments which show no evidence of significant crustal thickening during the grenvillian orogeny along a transect across the grenville front eastern region significant offsets of grenvillian paleopressure levels indicate that the thickened crust is a stack of imbricated slices with vertical components of displacement in the order of several kilometres after compensating for the grenvillian movement along the appropriate shear zones offsets remain between some of the archaean paleopressure levels suggesting that delamination of the archaean crust was initiated prior to the peak of grenvillian metamorphism the thrust slices thus identified in the eastern region have thicknesses of a few kilometres but they could be much thinner in the western region here the grenville front is ill defined and lies in a zone of gradual transition between the pontiac group metasediments of the superior province and the lac lambert migmatites of the grenville province the overall deformations of the two regions southeast of the grenville front are incompatible and cause the development of an intervening shear zone although the two regions experienced different tectonometamorphic histories they both belong to the parautochthonous belt of the grenville orogen

internally consistent recalibrations of mineral equilibria for geothermobarometry involving garnet orthopyroxene plagioclase quartz assemblages and their application to the south indian granulites abstract three reactions are calibrated as geothermobarometers for garnet orthopyroxene plagioclase quartz assemblages namely 1 2 ferrosilite 1 3 pyrope 1 2 enstatite 1 3 almandine a ferrosilite anorthite 2 3 almandine 1 3 grossularite quartz b and enstatite anorthite 2 3 pyrope 1 3 grossularite quartz c the internally consistent geothermobarometers based on reactions a b and c are calibrated from experimental data only the thermodynamic parameters of reaction a are derived from published experimental data in the fmas system n 104 in the range 700 1400 c and 5 50 kbar while those for reaction b are derived by summation of the existing reversed experimental data of the mineral equilibria ferrosilite fayalite quartz d and anorthite fayalite 2 3 almandine 1 3 grossularite e the retrieved thermodynamic parameters for reactions a b and c are respectively h0 cal 3367 209 2749 350 and 3985 545 s0 cal k 1 1 634 0 163 8 644 0 298 and 5 376 0 391 and v01 298 cal bar 1 0 024 0 60946 and 0 5614 on a one cation basis the derived margules parameters of the ternary ca fe mg in garnet are wfe mg 1256 1 0 0 23 t k wmg fe 2880 1 7 0 13 t k wca mg 4047 77 1 5 t k wmg ca 1000 77 1 5 t k wca fe 723 0 332 0 02 t k wfe ca 1090 cal and the ternary constant c123 4498 1 516 0 265 t k cal subregular solution model of non ideal mixing and fe mg al in orthopyroxene wfe mg 948 200 0 34 0 10 t k wfe al 1950 500 and wmg al 0 cal regular solution model of non ideal mixing the anorthite activity in plagioclase is calculated by the al avoidance model of subregular ca na mixing commonly used for geobarometry based on reactions b and c when the geothermobarometers are applied to garnet orthopyroxene plagioclase quartz assemblages n 45 of wide compositional range from the precambrian south indian granulites temperature ranges of 690 860 c x 760 45 c and pressure ranges of 5 10 kbar were obtained the p t values were estimated simultaneously and there is no difference in the pressure calculated from pmg reaction c and pfe reaction b in the existing calibrations this difference is 1 kbar or more furthermore there is no compositional dependence of the ln k of the experimental data in the fmas n 104 and the cfmas n 78 systems at different temperatures and the estimated temperatures of the south indian granulites

mineralogy and pressure temperature time path of cretaceous granulite gneisses south eastern san gabriel mountains southern california mid cretaceous granulite gneisses crop out in a narrow belt in the cucamonga region of the south eastern foothills of the san gabriel mountains southern california interlayered mafic granulites and pelitic carbonate calc silicate and quartzofeldspathic metasediments record hornblende granulite subfacies metamorphism at approximately 8 kbar and 700 800 c regional deformation and formation of banded gneisses ceased by c 108 ma although mafic intermediate magmatism and high grade metamorphism continued locally as late as c 88 ma garnet zoning in metapelitic gneisses suggests that peak metamorphism was followed locally by a period of near isobaric cooling but this interpretation requires diachronous cooling of the granulite belt which cannot be demonstrated without detailed thermo chronological data it is more likely that the entire terrane remained at granulite facies p t conditions until 88 ma followed by rapid uplift associated with juxtaposition against adjacent middle and upper crustal arc terranes uplift occurred between c 88 and 78 ma at rates of approximately 1 2 km ma 1 the geotectonic evolution of the cucamonga granulites is similar to mid cretaceous high p granulites in the sierra nevada and salinian block of central california late cretaceous uplift common to these granulites may provide an important tectonic link between dismembered mesozoic batholithic terranes in the california cordillera

phase relations between ca 3 fe 2 3 si 3 o 12 fe 3 2 fe 2 3 si 3 o 12 garnet and cafesi 2 o 6 fe 2 si 2 o 6 pyroxene solid solutions

streamflow regulation and multi level flood plain formation channel narrowing on the aggrading green river in the eastern uinta mountains colorado and utah abstract the style and degree of channel narrowing in aggrading reaches downstream from large dams is dependent upon the dominant geomorphic processes of the affected river the magnitude of streamflow regulation and the post dam sediment transport regime we measured different magnitudes of channel adjustment on the green river downstream from flaming gorge dam ut usa that are related to these three factors bankfull channel width decreased by an average of about 20 in the study area in reaches with abundant debris fans and eddy deposited sand bars the amount of channel narrowing was proportional to the decrease in specific stream power the fan eddy dominated reach with the greatest decrease in stream power narrowed by 22 while the reach with the least decrease in stream power narrowed by 11 in reaches with the same magnitude of peak flow reduction meandering reaches narrowed by 15 to 22 and fan eddy dominated reaches narrowed by 11 to 12 specific stream power was not significantly affected by flow regulation in the meandering reaches in the diverse array of reach characteristics and deposit types found in the study area all pre and post dam deposits are part of a suite of topographic surfaces that includes a terrace that was inundated by rare pre dam floods an intermediate bench that was inundated by rare post dam floods and a post dam floodplain that was inundated by the post dam mean annual flood analysis of historical photographs and tree ring dating of tamarix sp shows that the intermediate bench and post dam floodplain are post dam landforms in each reach type although these two surfaces occur at different levels they are forming simultaneously during flows of different magnitude and while the relative elevation and sedimentologic characteristics of the deposits differ between meandering reaches and reaches with abundant debris fans and eddies both reach types contain deposits at all of these topographic levels the process of channel narrowing varied between fan eddy dominated and meandering reaches in the meandering reaches where stream power has not changed narrowing was accomplished by essentially the same depositional processes that operated prior to regulation in fan eddy dominated reaches where significant reductions in stream power have occurred channel narrowing has been accompanied by a change in dominant depositional processes mid channel sand deposits are aggrading on deposits that in the pre dam era were active gravel bars these deposits are creating new islands and decreasing the presence of open framework gravel bars in eddies bare sand bars are replaced with vegetated bars that have a simpler topography than the pre dam deposits

heavy mineral analysis and provenance of yellow river sediments around the china loess plateau abstract in its upper middle reaches the yellow river has high sand contents after traversing through large areas of desert and the china loess plateau understanding riverbed sediment composition in the channel is critical for the interpretation of the potential provenance aeolian sand transport and the linkage between the loess plateau and the yellow river to address these issues we collected 52 samples from the modern riverbed proximal deserts and major tributaries and used analyses of grain size grain morphology and heavy mineral compositions to establish the spatial distribution and characteristics of source regions and riverbed sediments the heavy mineral assemblages demonstrate significant variations for the different sections of the yellow river the riverbed samples from the upper reach are dominated by opaque minerals limonite and magnetite amphibole and epidote with minor zircon tourmaline and rutile riverbed sediments from the middle reach are garnet rich reflecting the widespread distribution of mesozoic sandstones this variability closely reflects the source regions our data show that seasonal tributaries the ten great gullies carrying detritus from the ordos plateau may account for the localized high garnet concentrations in the inner mongolia section of the upper reach scanning electron microscope sem imaging of quartz grains show that the river sediments are characterized by composite microtextures acquired in both fluvial and eolian environments of the hedong ulan buh and kubuq deserts the mineralogical composition in the upper reach lanzhou yinchuan is similar to that of sediments in the loess plateau and northeast tibet plateau western lanzhou however the composition differs markedly from that in the inner mongolia section of the upper and middle reaches this variation indicates that in the upper reach the northeast tibet plateau contributes significant volumes of sediment to the yellow river and loess plateau but compositions change across the inner mongolia section of the upper and middle reaches owing to local sediment supply from arid desert areas and seasonal tributaries

suspended sediment transport response to upstream wash load supply in the sand bed reach of the upper yellow river china summary wash load is a major component of suspended sediment transport in the sand bed reach of the upper yellow river china this wash load sediment originates from the loess region with the high runoff mainly originating from the rock mountains of its upstream basin these characteristics result in a mismatch between water and sediment sources and a low probability of high runoffs meeting high suspended sediment concentration ssc flows as a result higher runoff with lower ssc levels hr ls and lower runoff with higher ssc values hs occur whose sscs do not follow the typical power form for flow discharges c i q where c i and q are ssc and flow discharge respectively here we modify the traditional power form with an upstream wash load supply function c 1 to satisfy the relation between the water and wash load sediment concentrations in water sediment mismatched cases c i q c 1 where c is an input flow s ssc using the daily flow discharges and sscs of nine typical hr ls flows and 18 hs flows in our study reach from 1960 to 2012 we find that changes in response to input flow conditions and downstream transport distances when the downstream transport distance is between 360 and 663 5 km varies between 0 3 and 0 6 in a hs input flow condition while in the hr ls input flow case tends to be greater than 0 6 between 0 74 and 0 65 the entrainment rate of an hr ls flow and the deposition rate of an hs flow appear to be asymmetrically balanced establishing a primary mechanism for channel aggradation and upward fining of floodplains in our study reach

the contribution of aeolian processes to fluvial sediment yield from a desert watershed in the ordos plateau china in arid zones many active aeolian dunes terminate at ephemeral and perennial desert rivers the desert rivers show very high rates of sediment transport that cause deleterious downstream effects on the river system and ecology high sediment loading has been attributed to severe water erosion of sparsely covered watersheds during infrequent but heavy rainfall although aeolian erosion is known to lead to high rates of wind blown sand transport direct confirmation of whether the aeolian processes accelerate or inhibit fluvial sediment loss is lacking here we show that an aeolian fluvial cycling process is responsible for the high rate of suspended sediment transport in a sudalaer ephemeral desert channel in the ordos plateau of china frequent aeolian processes but low frequency once every 3 years on average flooding occur in this region wind blown saltating grains appeared to be unable to cross the desert channel because of interruption of channel induced recirculating air flow and therefore tended to settle in the channel during the windy seasons leading to channel narrowing during flooding this narrowed channel was found to yield a threefold increase in suspended sediment loading and a 3 4 fold increase in the weight percentage of the 0 08 0 2 mm sediment fraction on 18 july 2012 loss of stored aeolian sand due to channel erosion accounted for about half of the total sediment yield in this watershed these findings show that aeolian processes play an essential role in accelerating the sediment yield from a watershed characterized by aeolian fluvial interplay and also suggest that the drier the region and the greater the aeolian process the more the aeolian process contributes to fluvial sediment yield copyright 2013 john wiley sons ltd

metamorphic geology and regional geothermobarometry of a grenvillian massif the long range inlier newfoundland abstract geothermobarometry of middle proterozoic amphibolite to granulite facies gneiss of the long range inlier reveals a southwestward increase in metamorphic temperature from 600 650 c to nearly 800 c at a pressure between 5 and 8 kbar throughout the massif a steep d p d t slope of 14 bars c 1 determined using the garnet orthopyroxene plagioclase quartz thermobarometer indicates fairly rapid uplift of the inlier and or records the effects of a late grenvillian 970 ma tectonothermal overprint grenvillian granitoid rocks and a mafic pluton of unknown age have narrow thermal aureoles and intruded the gneiss complex following regional high grade metamorphism metamorphic conditions of the adjacent grenville province span those determined for the long range inlier available data suggest that both areas were uplifted from moderate crustal levels during the middle to late proterozoic and indicate negligible differential uplift of the inlier relative to the grenville province during paleozoic orogenies

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

discharge and sediment supply controls on erosion and deposition in a dynamic alluvial channel research on dynamic alluvial channels has recognised the influence on river channel change of both discharge and sediment supply although it has proved difficult to measure the latter this paper presents the first accurate data from a dynamic alluvial channel that describe the interrelated effect on channel morphological change of both discharge and sediment supply variations over different timescales reliable information on the spatial patterns of erosion and deposition were obtained using combined photogrammetry and tacheometric survey of the meltwater stream of a glacierised catchment over a 5 week period over the full time period the morphological evidence suggested the passage of a wave of sediment counter intuitively the period of aggradation was associated with increasing diurnal peak and base flow discharge magnitude while degradation occurred during a period of steady peak diurnal discharge this suggests that the channel change was controlled by variation in upstream sediment supply over a shorter timescale information on diurnal changes in morphology reveals that although discharge was responsible for some aspects of channel change this was modified by the effects of upstream sediment supply consideration of the spatial patterns of erosion and deposition at the within reach scale reinforces this point with spatial aspects of morphological change being driven by discharge and sediment supply fluctuations but modified by spatial feedbacks associated with internal channel morphology the implications of these findings for fluvial geomorphology in general are considered

geochemistry of exposed granulite facies terrains and lower crustal xenoliths in mexico the trace element compositions of 13 samples from exposed granulite facies terrains and 17 granulitic lower crustal xenoliths were determined using an inductively coupled plasma mass spectrometer to constrain the composition and evolution of the mexican lower crust most xenoliths found are pyroxeneplagioclase orthogneisses although quartzo feldspathic paragneisses form up to 50 of the xenolith population in some areas lithologies in the exposed terrains consist of pelitic and carbonate rich paragneisses charnockites and less abundant basic intermediate and felsic orthogneisses both xenoliths and exposed granulites generally have low abundances of incompatible elements such as k rb th and u the xenoliths however often have lower abundances of these elements than the exposed granulites high k rb ratios coupled with an inverse correlation between k2o and k rb indicate that most samples from the mexican lower crust are depleted in both k and rb furthermore th u ratios similar to upper crustal materials and high la th ratios suggest depletion in both th and u relative to average crustal material removal of a melt phase either after the crystallization of cumulates or following a partial melting event can explain many of the chemical features observed and may be responsible for the elemental depletions some samples however appear to have been unaffected during their residence in the lower crust and chemically resemble their presumed protoliths available geobarometric data suggest that xenoliths equilibrated near the crust mantle boundary 10 kbar and represent the lowermost crust while the exposed granulites equilibrated at shallower crustal levels 7 kbar thus the differences observed between the xenoliths and exposed granulites indicate that there may be chemical and lithologic zonation in the mexican lower crust the lowermost crust in mexico consists of crystallized basaltic liquids cumulates and or residue after the removal of a partial melt as well as garnet rich metasediments

high pressure metamorphism in the western cordillera of north america the skagit gneiss a major component of the crystalline core of the north cascades was metamorphosed during a mid cretaceous to early tertiary high p event driven by the collision of the insular and intermontane superterranes maximum pressures recorded by metapelitic rocks are 8 10 kbar at 650 725 c high pressures are also indicated by coexisting staurolite and hornblende in amphibolites in the skagit gneiss and adjacent cascade river schist mineral reactions continued during nearly isothermal decompression from 8 10 kbar to c 3 5 kbar early high p minerals e g kyanite are present as armoured relics in garnet in gneisses that contain sillimanite and cordierite in the groundmass skeletal relics of kyanite are also present in the groundmass of lower grade staurolite bearing schists that contain texturally later cordierite this matrix kyanite may have been preserved as a result of rapid uplift following initial decompression at high temperature these results represent a revision of the metamorphic history of the skagit gneiss which was formerly thought to have experienced only relatively low p barrovian metamorphism qualitative estimates of metamorphic conditions based on stable matrix mineral assemblages result in an underestimation of maximum pressures because mineral reactions continued during decompression geobarometric results for the skagit gneiss are interpreted as evidence for major crustal thickening in the north cascades recognition that pressures of c 9 kbar were attained supports a contractional model for north cascades orogenesis and requires that tectonic syntheses account for the burial of the skagit gneiss protoliths to a depth of c 25 30 km

complex behaviour of natural sediment carrying streamflows and the geomorphological implications based on the data from alluvial rivers in china the complex mechanical behaviour of sediment carrying streamflow of natural rivers has been observed channel geometry also exhibits complex behaviour in response to variation in suspended concentration with the increase in suspended concentration channel width depth ratio increases reaches a maximum and then decreases the inverse is true for channel sinuosity when suspended concentration is low a meandering pattern is dominant the increase in suspended concentration leads to a transformation from a meandering to a braided pattern but when the suspended concentration increases further and enters the range of hyperconcentrated flows the meandering pattern appears the complex behaviour of channel pattern change may be regarded as a reflection of the complex behaviour of sediment carrying streamflows at the river reach scale copyright c 2002 john wiley sons ltd

channel incision on the lower american river california from streamflow gage records channel incision along the lower american river from 1905 to 1995 is investigated using channel cross section plots and statistical analysis of stage discharge data from two streamflow gages located at three sites channel incision lowered thalweg elevations at rates of up to 8 2 cm yr 1 and flow stages decreased at rates of up to 4 3 cm yr 1 for periods lasting several decades at a critical flood risk location in sacramento flow stages lowered 2 m from 1924 to 1970 channel incision was the result of channel recovery from aggradation due to hydraulic gold mining sediment and was exacerbated by sediment storage behind dams prolonged erosion and transport of historical alluvium in this river suggest that g k gilbert s symmetrical sediment wave model is inappropriate for the lower american river and may not adequately allow for the importance of sediment storage and remobilization in fluvial systems

reaction spaces and p t paths from amphibole eclogite to greenschist facies in the austroalpine domain oetztal complex the transition from feldspar amphibolite to eclogite is a very wide p t field that extends from some where close to 5 kbar where the garnet amphibole pair starts to appear to 10 20 kbar at albite out reaction then up to 25 30 kbar where an hydrated phase such as amphibole can be stable with pyroxene and garnet thus the assemblage garnet py amphibole tr epidote cz plagioclase ab clinopyroxene di quartz qz fluid is commonly reported in a large number of metamorphic terrains these mineral phases are complex solid solutions which adapt to variations in environmental conditions mainly by means of continuous reactions the reaction space introduced by thompson in 1982a provides a very elegant and powerful tool to approach these high variance assemblages the reactions

channel adjustments to historical disturbances along the lower brazos and sabine rivers south central usa historical channel adjustments are documented and discussed in context with anthropogenic disturbances along two meandering coastal plain rivers the lower brazos and sabine rivers in the south central united states hard copy streamflow measurement notes of the u s geological survey were utilized to render historical cross sections 1925 2007 at nine gauging stations which were complemented with repeat photographs and flood frequency analysis to assess trajectories of channel change and interpret causative mechanisms downstream and upstream propagating disturbances caused episodes of channel bed incision and aggradation at different locations for distinct time periods along both rivers incision associated with upstream dams is detected but channels are compensated downstream with sediment inputs from lateral channel migration and tributaries in one case temporary aggradation along the brazos river at waco was likely caused by a combination of dam construction and regional soil erosion channel bed incision on the lowermost brazos river is unrelated to dams but is associated with instream aggregate extraction possibly in conjunction with downstream channelization on the sabine river extensive aggradation during the 1930s might be associated with logging activities 1880s 1930s but whether the cause is pervasive regional scale hillslope erosion or local scale mill site activities is indeterminate following passage of this sediment the river generally recovered to pre disturbance conditions and has exhibited stability despite a mainstem reservoir translation of this sediment slug is attenuated by a transition to a flood prone distributary dominated system downstream of the holocene pleistocene terrace onlap position additional findings include cross channel hingepoints separating thalweg incision from simultaneous point bar or bank accretion at meander bends which indicates channel adjustment occurs along non cohesive beds in preference to cohesive or artificially reinforced banks also flood reduction has resulted in bankfull stages that are higher than levels associated with the post regulation 2 year return period finally vegetation encroachment along banks since the 1970s coupled with reduced flooding along the lower brazos river has promoted bank accretion deposits that when fully developed serve as morphologic indicators of the post regulation 1 to 2 year return period stage

pressure temperature evolution of metapelitic granulites in a polymetamorphic terrane the rauer group east antarctica distinctive lithological associations and geological relationships and initial geochronological results indicate the presence of an areally extensive region of reworked archaean basement containing polymetamorphic granulites in the rauer group east antarctica structurally early metapelites from within this reworked region preserve complex and varied metamorphic histories which largely pre date and bear no relation to a late proterozoic metamorphism generally recognized in this part of east antarctica in particular magnesian metapelite rafts from long point record extreme peak p t conditions of 10 12 kbar and 100 1050 c and an initial decompression to 8 kbar at temperatures of greater than 900 c initial garnet orthopyroxene sillimanite assemblages contain the most magnesian and pyrope rich garnets xmg 0 71 yet found in granulite facies rocks a high temperature decompressional p t history is consistent with reaction textures in which the phase assemblages produced through garnet breakdown vary systematically with the initial garnet xmg composition reflecting the intersection of different divariant reactions in rocks of varied composition as pressures decreased this history is thought to relate to archaean events whereas a lower temperature c 750 800 c decompression to 5 kbar reflects late proterozoic reworking of these relict assemblages the major late proterozoic c 1000 ma granulite facies metamorphism is recorded in a suite of younger fe rich metapelites and associated paragneisses in which syn to post deformational decompression through 2 4 kbar from maximum recorded p t conditions of 7 9 kbar and 800 850 c is constrained by geothermobarometry and reaction textures this p t evolution is thought to reflect rapid tectonic collapse of crust previously thickened through collision

exhumation of high pressure metamorphic rocks during crustal extension in the d entrecasteaux region papua new guinea the d entrecasteaux islands of eastern papua new guinea consist of a number of active metamorphic core complexes formed under an extensional tectonic setting related to sea floor spreading in the west woodlark basin the complexes are defined by mountainous domes 2500 m high of fault bounded high grade metamorphic rocks including eclogite facies intruded by 2 4 ma granodiorite plutons garnet clinopyroxene exchange thermometers indicate that the temperature of equilibration of the eclogites was 730 900 c the jadeite component of omphacite indicates minimum pressure of 21 kbar suggesting depths of 70 km the metamorphic rocks have undergone widespread retrogression to amphibolite facies retrogression of the metamorphic basement is associated with shearing and formation of the metamorphic core complexes p t conditions in the early stages of shear zone activity determined using the garnet biotite exchange thermometer and the gasp and grips barometers were 570 730 c and 7 11 kbar a second phase of re equilibration at much lower pressures appears to be related to the widespread intrusion of granodiorite plutons one re equilibrated gneiss indicated maximum temperature of 730 c at estimated pressures of approximately 4 kbar this late high temperature metamorphism is also indicated by reactions involving the production of hercynite and corundum in aluminous gneisses and formation of sillimanite at the expense of kyanite two major episodes of granodiorite intrusion occurred during uplift and exhumation of the core complexes both closely coincide spatially with high temperature metamorphic rocks the onset of deformation in extensional shear zones and subsequent uplift of the metamorphic basement these observations indicate a fundamental link between uplift and granodiorite intrusion during continental extension and the formation of the d entrecasteaux islands metamorphic core complexes

the human role in changing river channels abstract direct consequences of the human role where human activity affects river channels through engineering works including channelization dam construction diversion and culverting have been long recognised marsh 1864 thomas 1956 the less obvious indirect effects of point and reach changes occurring downstream and throughout the basin however are much more recently appreciated dating from key contributions by strahler strahler a n 1956 the nature of induced erosion and aggradation in w l thomas ed man s role in changing the face of the earth university of chicago press chicago 621 638 wolman wolman m g 1967 a cycle of sedimentation and erosion in urban river channels geografiska annaler 49a 385 95 schumm schumm s a 1969 river metamorphosis proceedings american society of civil engineers journal hydraulics division 95 255 73 and graf graf w l 1977 the rate law in fluvial geomorphology american journal of science 277 178 191 these are complemented by effects of alterations of land use such as deforestation intensive agriculture and incidence of fire with the most extreme effects produced by building activity and urbanisation changing river channels are most evident in the channel cross section where changes of size shape and composition are now well established with up to tenfold increases or decreases illustrated by results from more than 200 world studies in addition the overall channel planform the network and the ecology have changed specific terms have become associated with changing river channels including enlargement shrinkage and metamorphosis although the scope of adjustment has been established it has not always been possible to predict what will happen in a particular location because of complex response and contingency the ways in which changes in cross section relate to reach and network changes are less clear despite investigations showing the distribution of changes along segmented channels when considering the human role in relation to changing river channels at least five challenges persist first because prediction of the nature and amount of likely change at a particular location is not certain and because the contrasting responses of humid and arid systems needs to be considered modelling is required to reduce uncertainty as was first emphasised by burkham burkham d e 1981 uncertainties resulting from changes in river form american society civil engineers proceedings journal hydraulics division 107 593 610 second feedback effects incorporated within the relationship between changes at channel reach and network scales can have considerable implications especially because changes now evident may have occurred or have been initiated under different environmental conditions third consideration of global climate change is imperative when considering channel sensitivity and responses to threshold conditions fourth channel design involving geomorphology should now be an integral part of restoration procedures this requires fifthly greater awareness of different cultures as a basis for understanding constraints imposed by legislative frameworks better understanding of the ways in which the perception of the human role in changing river channels varies with culture as well as varying over time should enhance application of design for river channel landscapes

a model to study the grain size components of the sediment deposited in aeolian fluvial interplay erosion watershed abstract aeolian fluvial interplay erosion areas with complex dynamics and physical sources are the main suppliers of coarse sediment in the yellow river understanding the composition distribution and sources of deposited sediments in such areas is of great importance for the control of sediment transport in rivers in this paper a typical aeolian fluvial interplay erosion watershed the dongliu gully was studied and the frequency distribution curves of sediments deposited in the stream channel were fitted using the weibull function sources of deposited sediment in the stream channel were analyzed based on the law of the conservation of matter results showed that the hilly zone accounted for 78 of deposited sediments which were dominated by material with a median grain size d 50 of 0 093 mm and the desert zone accounted for 22 of deposited sediments which were dominated by material with a d 50 of 0 01 mm wind erosion dynamics accounted for 72 of deposited sediments while water erosion dynamics accounted for only 28 this research provides a theoretical basis for the control and management of rivers with high sediment content

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

hercynian tectonometamorphic evolution of the bosost dome french spanish central pyrenees metamorphic and structural studies show that the bosost dome central pyrenees is a metamorphic as well as a structural dome developed in cambro ordovician to devonian metasediments around a migmatitic core during the hercynian orogeny the structural metamorphic dome occurs in epizonal terranes and is twice as large as originally described the structural dome shows a concentric zoning of d2 and d3 local deformations developed around the migmatites and superimposed on the d1 regional hercynian deformation the structural data suggest that migmatites were emplaced diapirically into palaeozoic metasediments during d1 and are responsible for the local d2 and d3 deformations an early medium pressure high temperature metamorphism occurred during d1 leading to anatexis under water rich conditions then evolved progressively to a high temperature low pressure metamorphism during the d2 and d3 deformations the corresponding p t time path is a clockwise loop representing the evolution of the metamorphism from migmatiza tion to the diapiric emplacement of migmatites in a compressional setting pressure values obtained from geobarometry are three times as high as expected from sedimentological data this suggests that the hercynian metamorphism developed in a thickened crust during the n s shortening responsible for the large scale e w folding observed throughout the pyrenean axial zone

short and long term changes to bed mobility and bed composition under altered sediment regimes altered flow and sediment transport regimes from impoundment can result in significant channel bed composition changes that exacerbate the geomorphic and ecological effects of flow regulation using long term discharge and cross sectional data in combination with a two fraction sediment transport model we assess changes in the downstream bed of two flow regulated rivers with equivalent dam induced changes in flow but opposite changes in sediment flux supply limitation has led to incision and armoring in one case while supply excess has led to aggradation and embeddedness in the other under limited sediment supply bed elevation variability decreases soon after impoundment while excess sediment supply results in a decades long gradual decrease in both bed elevation variability and depth of incision although the balance of sediment supply and transport differs between dam management styles in both cases both the immediate and more gradual changes can be explained within the framework of a two fraction sediment transport model our results demonstrate the importance of considering bed composition on sediment transport predictions and the development of management strategies for ecosystem maintenance

ultra high temperature metamorphism of metapelitic granulites from kondapalle eastern ghats belt implications for the indo antarctic correlation a suite of quartz and corundum bearing metapelitic granulites intruded by layered gabbronorite pyroxenite anorthosite at kondapalle eastern ghats belt preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions in the quartz bearing associations the reactions are a biotite sillimanite quartz garnet liquid b garnet sillimanite spinel magnetite quartz c fe2tio4 o2 ferrian ilmenite magnetite d reversal of reaction b e fe2o3 rich ilmenite plagioclase quartz fe2o3 poor ilmenite garnet o2 reactions in the corundum bearing associations are f spinel biotite sillimanite garnet liquid g biotite sillimanite garnet ti rich spinel corundum liquid h biotite sillimanite garnet corundum liquid i fe2tio4 feal2o4 o2 ferrian ilmenite fe3o4 al2o3 in ilmenite j garnet corundum spinel sillimanite to examine the paragenetic evolution of the metapelitic granulites a petrogenetic grid for the kfmash system at high temperatures and pressures involving quartz and corundum was constructed the sequence of inferred reactions documents an anticlockwise heating cooling path reintegrated compositions of spinel with 10 mol fe2tio4 and feldspars indicate ultra high temperature uht of metamorphism 1000 c comparable with the liquidus temperature of the enclosing magmatic rocks crystallization pressures inferred for the magmatic rocks and the pressure constraints imposed by the petrogenetic grid on the metapelite assemblages indicate that the emplacement of the igneous suite and the accompanying uht metamorphism occurred in the lower crust 8 kbar reported u pb cooling ages of monazite and allanite from a late pegmatite suggest the uht metamorphism to be older than 1600 ma the deduced p t history and the absence of grenvillian high grade metamorphism in the study area provide important constraints on the configuration of east gondwana in particular on the continuation of the napier rayner terrane boundary into the eastern ghats belt