mafic magmas as sources for gold in middle miocene epithermal deposits of the northern great basin united states evidence from pb isotope compositions of native gold we measured the pb isotope compositions of traces of lead alloyed by gold electrum and naumannite and gangue vein minerals in bonanza epithermal gold deposits of the northern great basin and compared them to possible sources of lead in the region gangue minerals have pb isotope compositions consistent with hydrothermal leaching of lead from local host rocks lead isotope ratios of gold ores however have signatures that are distinct from the gangue minerals and common host rocks in the area such as metasediments and miocene rhyolites the gold ores are isotopically similar to local mafic rocks of the middle miocene bimodal volcanic assemblage indicating that the latter are the likely source of the precious metals the local mafic rocks are also similar to the middle miocene columbia river basalts suggesting that both were derived from a mantle source with similar pb isotope composition our preliminary results indicate that the precious metals were derived from mafic magmas likely related to northern nevada rifting processes and or to the arrival of the columbia river basalt plume and the emergence of the yellowstone hot spot exsolving volatiles from the mafic magmas most likely transported gold upward to the shallow meteoric water dominated epithermal systems where the precious metals precipitated together with quartz and adularia to form bonanza ores that typify these deposits

morphological and sedimentological responses of streams to human impact in the southern blue ridge mountains usa abstract morphological and sedimentological responses of streams to basin scale impact have been well documented for intensively agricultural or urban areas sensitivity thresholds of streams to modest levels of disturbance however are not well understood this study addresses the influence of forest conversion on streams of the southern blue ridge mountains a region that has received little attention with respect to human impact on stream channels basins were chosen for this study to represent the end members of the range of human impact in the area with the forest cover of the basin used as a proxy for level of impact ranging from about 70 100 regionally two pairs of lightly impacted 90 forest and moderately impacted 70 80 forest sub basins of the upper little tennessee river were identified for comparison reach characteristics e g slope drainage area and riparian cover were aligned in each pair to isolate contrasting forest cover as the primary driver of any detected differences in morphology and sedimentology a suite of standard cross sectional and longitudinal data was collected for each reach for characterization of the sedimentology and morphology of the streams difference of means tests were conducted to identify parameters significantly differing between the lightly and moderately impacted streams in both pairs consistent and significant differences within both pairs were demonstrated in bankfull width depth ratios baseflow wetted width and particle size on the stream bed both in the thalweg and throughout the channel bed the moderately impacted streams are narrower than the lightly impacted streams and the bed texture of the moderately impacted streams is finer than that of the lightly impacted streams the moderately impacted streams contain a higher percentage of

sources and petrogenesis of late triassic zhiduo volcanics in the northeast tibet implications for tectonic evolution of the western jinsha paleo tethys ocean abstract the western jinsha suture representing a branch of the paleo tethys makes the junction between the songpan ganzi complex and the north qiangtang block nqb however the triassic tectonic evolution of the western jinsha paleo tethys ocean is poorly constrained this paper shows new la icp ms zircon u pb geochronology major and trace elements and sr nd hf isotopic compositions of the zhiduo dacitic volcanic rocks in the northern margin of the nqb la icp ms zircon u pb dating displays that they erupted between 227 2 and 228 1 ma these rocks exhibit high silica medium k calc alkalic signature and low mgo tio2 p2o5 cr and ni compositions they are enriched in light rare earth elements and large ion lithophile elements with moderate to strong negative eu anomalies eu eu 0 24 0 56 and depleted in heavy rare earth elements and high field strength elements they possess relatively low initial 87sr 86sr ratios 0 7055 0 7084 positive whole rock end t 0 2 to 1 4 and magmatic zircon ehf t values focus on 9 2 2 7 with young nd and hf model ages t2dm nd 885 983 ma t2dm hf 467 1035 ma these features are comparable to those of typical arc volcanic rocks and indicate that they were probably derived from partial melting of a juvenile crust source the eruption of these volcanic rocks could be attributed to southward subduction of the western jinsha paleo tethys ocean in combination with previous studies we propose that the subduction of the western jinsha paleo tethys ocean initiated at the beginning of the late triassic ca 228 ma and closed at the end of the late triassic ca 208 ma in addition there is a universal northeastward younging trend of arc magmas in the northern margin of the nqb which may indicate a model involving the initial shallow subduction and subsequent slab roll back

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

sims u pb dating of vein hosted hydrothermal rutile and carbon isotope of fluids in the wulong lode gold deposit ne china linking gold mineralization with craton destruction abstract wulong is the largest lode gold deposit in the liaodong peninsula northeastern north china craton ncc gold mineralization mainly occurs in the quartz sulfide veins which are hosted in jurassic monzogranite and early cretaceous diorite dikes here rutile grains are firstly identified in the auriferous quartz pyrite vein the vein hosted rutiles have textural associations with quartz chlorite pyrite and bi sulfosalts and host fluid inclusions indicating that they are unequivocally of hydrothermal origin and co precipitate with gold the rutile grains are characterized by high w and v concentrations and u shaped rare earth elements pattern with the greatest depletion in mree due to excess zr incorporation during fast rutile crystal growth process from the f rich ore forming fluids zr in rutile thermometers provide unrealistic crystallization temperatures 550 c which are much higher than the previous homogenization temperatures data of fluid inclusions yu et al 2018 all these geochemical signatures also support that rutiles formed from the hydrothermal fluids the 13c values of co2 gases in low salinity aqueous carbonic fluid inclusions from the mineralized quartz range from 9 6 to 1 7 average 5 7 indicating mantle magmatic sources for the ore forming fluids sims u pb dating yields a more precise and robust age of 122 3 1 1 ma n 23 mswd 0 82 for the gold mineralization at wulong this new date is roughly coeval with the ore hosted diorite dikes and the sanguliu granitic pluton most in 125 120 ma such close temporal association provides additional weights of evidence for a magmatic affinity to the gold formation regionally the rutile u pb age indicates that the gold mineralization occurs in an extensional tectonic regime caused by the thinning and destruction of the lithosphere beneath the ncc meanwhile the timing of gold mineralization is the same as the peak age of ncc destruction therefore we propose that the wulong deposit has a genetic link with this craton destruction this is similar to numerous other early cretaceous gold deposits across the ncc such as those in the xiaoqinling and jiaodong districts our study indicates that rutile is a robust u pb chronometer for the lode gold deposit but may be not a good geothermometer in the case of f rich hydrothermal fluid system

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

simulation of flow over pool riffle topography a consideration of the velocity reversal hypothesis computer flow simulations using the hec 2 step backwater routine are used to demonstrate the effect of systematically varying river channel width riffle spacing and channel roughness on the shear velocity section mean velocity and energy slope in fixed bed pool riffle sequences initial scaling is obtained by utilizing published information on hydraulic parameters within reaches of the river severn subsequently this restriction is relaxed and the effect of varying parameter combinations within realistic limits is explored the purpose of this exercise is to isolate those scenarios which may preclude or promote the occurrence of a competence reversal such that pools scour at high flow whilst deposition occurs on riffles it is concluded that rivers in which pools are hydraulically rougher than riffles are likely to demonstrate a competence reversal for prescribed conditions the critical discharge at which a reversal occurs is a negative function of riffle spacing and riffle width relative to pool width downstream variation in hydraulic roughness also has implications for the phase relationship of shear velocity maxima and minima in relation to the extremes in pool riffle topography

wildfire morphologic change and bed material transport at fishtrap creek british columbia abstract in 2003 a wildfire burned nearly two thirds of the fishtrap creek watershed including the forested floodplain annually repeated surveys of the stream channel combined with bed material tracer studies in 2006 and 2007 indicate that the channel has become unstable and that the bed material transport dynamics have changed since the fire using these data the morphologic changes have been quantified and event scale bed material transport rates have been estimated for four post fire freshets the immediate response of the channel during the 2005 and 2006 freshets was a progressive shift in channel morphology from a relatively featureless plane bed morphology devoid of significant sediment accumulations to a riffle pool morphology in which bars cover a significant proportion of the bed this transformation occurred in association with moderate bed material sediment transport rates and only minor bank erosion within the study reach extensive bank erosion occurred during the 2007 and 2008 freshets producing a dramatic change in channel morphology and increasing the local bed material transport rates by an order of magnitude post fire monitoring of streamflow and suspended sediment concentrations a surrogate for upstream sediment supply indicates that post fire increases are not detectable presented in eaton et al in press and our analysis demonstrates that major morphologic changes can occur following wildfire even when the common external drivers of stream discharge and sediment supply remain unchanged

equilibrium pool dimensions and sediment sorting patterns in coarse grained new england channels abstract pools and riffles are natural bedforms that produce variations in width and depth along channels deemed critical for aquatic habitat an understanding of this morphology is necessary for the successful design of a reconstructed or restored channel to better understand pool geometry and sorting characteristics of new england channels characterizations of pool geometry were performed on 145 different pools strongly influenced by channel constrictions characterizations of channel bed sediments were also performed at 34 of these locations data from 120 pools were used in least squares multiple regression analysis with 19 different independent variables to develop prediction equations for pool depth length and exit slope gradient these equations were then tested using the 25 remaining pools eighteen different geometric variables were then used to predict sediment 50 values in pool centers pool exit slopes and riffles for the subset of 34 samples the regression analyses for pool geometry indicate that pool depth is significantly influenced to a decreasing degree by pool exit slope width constriction gradient constriction width drainage area upstream channel width and the exit slope expansion ratio with an r 2 value of 0 53 similarly pool length is influenced by channel gradient location of the channel constriction pool width drainage area and constriction length with an r 2 value of 0 72 the gradient of pool exit slope is influenced by drainage area channel gradient and constriction gradient with an r 2 value of 0 34 however r 2 values for exit slope increased to 0 65 when sediment d 50 data were utilized using the resulting regression equations to predict dimensions for the 25 verification pools yields average residuals near zero although moderate variations do exist a tukey kramer hsd comparison of the means for sediment 50 values indicates pool sediments are significantly coarser than pool exit slope and riffle sediments for the subset of 34 pools regression analyses also suggest significant relations between the size of sediments in pools and riffles and a combination of geometric variables with r 2 values that range from 0 45 to 0 62 the results suggest that pool dimensions are related to basin wide variability and local hydraulic conditions the findings also suggest that the characteristics of constrictions and the downstream section of pools provide an important control on scouring and sorting characteristics throughout the pool riffle morphology

the cretaceous huangdaoshan cu bearing intrusion in chuzhou petrogenesis and implications for the cu mineralization in the middle lower yangtze river valley metallogenic belt eastern china abstract the huangdaoshan mineral deposit in the middle lower yangtze river valley metallogenic belt is located on the northern margin of the yangtze craton eastern china it is hosted by the high k calc alkaline quartz monzonite porphyry and quartz diorite porphyry of huangdaoshan intrusion the molybdenite re os age for the mineral deposit suggests that mineralization occurred at 128 9 2 3 ma and was coeval with the ore bearing intrusion 130 1 ma both porphyries are enriched in light rare earth elements lree and large ion lithophile elements lile depleted in heavy rare earth elements hree and high field strength elements hfse and have positive eu anomalies they also show adakitic affinities with high sr 914 1227 ppm and sr y ratios 125 212 and low y 5 40 9 00 ppm and yb 0 46 0 75 ppm contents petrography micro fabric features and sr nd hf isotopic results suggest that these adakite like magmas were derived from magma mixing between mantle and crustal derived materials the strong ree fractionations as well as the high la sm 6 0 7 1 and intermediate sm yb 4 5 5 6 ratios suggest that hornblende crystallization was the dominant control on fractionation apparent temperatures based on ti in zircon thermometry show that the mineralization related porphyries crystallized at 711 c 790 c the oxygen fugacity fo2 estimated from hornblende mg contents and biotite fe3 fe2 and mg contents indicates that the mineralized magma possessed a high oxidation state nno 0 15 to nno 1 62 the geochemical characteristics of the intrusions enrichment in liles depletion in hfses and nb ta anomalies indicate that the mafic magma was derived from partial melting of the enriched lithosphere mantle which had been metasomatized by slab derived fluids from a subducted oceanic plate therefore the parental magma contained high contents of h2o and metal e g cu with high fo2 the extensive contemporaneous magmatism metallogenic events and volcanic basins in the region suggest an extensional tectonic setting we further correlated this extension regime with slab roll back of the paleo pacific plate

formation and maintenance of a forced pool riffle couplet following loading of large wood abstract pool riffle maintenance has been documented in numerous studies but it has been almost impossible to characterize detailed natural pool riffle formation mechanisms because of the lack of baseline data prior to pool establishment in 2013 a study was conducted on the blackledge river in connecticut to document the formation of a new pool riffle couplet on a section of river that had previously been studied from 1999 to 2001 in 2001 the study reach contained a scour hole with a residual depth of 0 08 0 09 m downstream of a 1930s paired deflector with no identifiable riffle immediately downstream at this time a large severely undercut hemlock tree was noted along the left bank sometime between fall 2001 and 2004 the tree fell perpendicular to flow across the channel and formed a large wood lw jam and new pool riffle couplet several meters downstream of the old scour hole pool spacing along the reach decreased from 4 47 bankfull widths bfw in 1999 to 3 83 bfw after the new pool riffle couplet formed the new pool has a residual depth the water depth of the streambed depression below the elevation of the immediate downstream hydraulic control of 1 36 0 075 to 1 59 0 075 m which resulted from a combination of 1 32 0 09 m or less of incision below the old scour hole 95 6 or less of the depth increase and up to 0 18 0 09 m of downstream deposition and associated backwater formation 13 2 or less of the depth increase to assess dynamic stability of the pool riffle couplet over several flood cycles surficial fine sediment and organic material along the reach were quantified the 23 m long pool stores 25 7 of the surficial fine grained sediments and 15 4 of organic material along a 214 m long reach that includes one additional artificially created pool an adjacent 50 m long secondary channel impacted by the lw jam stores 65 3 of the surficial fine grained sediments and 54 8 of organic material along the full reach

sediment deposition and transport patterns following a reservoir sediment release a reservoir sediment release on the north fork poudre river supplied 7000 m3 of silt to pebble sized sediment to an originally boulder bed channel deposition along the 12 km of channel downstream from the reservoir occurred primarily in pools during the subsequent snowmelt hydrograph sediment was progressively scoured from the upstream and then the downstream pools initial sediment reworking in the pools created a deep narrow thalweg scoured to the original pool bed with additional sediment deposition in lateral eddies continued reworking reduced but did not completely remove these eddy deposits the channel became supply limited with respect to finer grain sized fractions clay to medium sand first at upstream and then at downstream sites and eventually became supply limited with respect to coarser grain sized fractions coarse sand to pebbles bedload transport rates at a site were strongly linked to the depletion of sediment stored in upstream pools magnitude duration and sequence of flows were all important controls on bedload transport and return of the channel to its prerelease state

evidence for regional stream aggradation in the central oregon coast range during the pleistocene holocene transition abstract low nearly continuous terraces of similar age are present along streams in drainage basins that range in size from drift creek 190 km 2 to the umpqua river 11 800 km 2 in the oregon coast range radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000 11 000 14 c yr b p beveled bedrock surfaces straths that underlie the fluvial sediments are 1 8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied where exposed the bedrock straths are overlain by 2 11 m of fluvial sediment that consists of a bottom stratum channel facies of sandy pebble cobble gravel and a top stratum overbank facies of sandy silt or silt eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in coast range drainage basins during the pleistocene holocene transition the cause of such widespread aggradation is unknown but may be related to climate induced changes in the frequency of evacuation of colluvium from hollows which are common in all drainage basins in the region

unifying criterion for the velocity reversal hypothesis in gravel bed rivers it has been hypothesized that velocity reversals provide a mechanism for maintaining pool riffle morphology in gravel bed rivers an important habitat for salmonids which are at risk in many places worldwide and that are the focus of extensive environmental legislation in europe and north america however the occurrence of velocity reversals has been controversial for over 3 decades we present a simple one dimensional criterion that unifies and explains previous disparate findings regarding the occurrence of velocity reversals results show that reversal depends critically on the ratio of riffle to pool width residual pool depth difference between pool and riffle elevations and on the depth of flow over the riffle suggesting that land management activities which alter channel form or divert water from the channel can have negative impacts on the sustainability of pool riffle habitat in gravel bed rivers

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

effects of sediment pulses on bed relief in bar pool channels to further develop prediction of the range of morphological adjustments associated with sediment pulses in bar pool channels we analyze channel bed topographic data collected prior to and following the removal of two dams in oregon marmot dam on the sandy river and brownsville dam on the calapooia river we hypothesize that in gravel bed bar pool channels the response of bed relief to sand and gravel sediment pulses is a function of initial relief and pulse magnitude modest increases in sediment supply to initially low relief sediment poor cross sections will increase bed relief and variance of bed relief via bar deposition modest increases in sediment supply to initially high relief cross sections characteristic of alternate bar morphology will result in decreased bed relief and variance of relief via deposition in bar adjacent pools these hypothesized adjustments are measured in terms of bed relief which we define as the difference in elevation between the pool bottom and bar top we evaluate how relief varies with sediment thickness where both relief and mean sediment thickness at a cross section are normalized by the 90th percentile of observed relief values within a reach prior to a sediment pulse field measurements generally supported the stated hypotheses demonstrating how introduction of a sediment pulse to low relief reaches can increase mean and variance of relief while introduction to high relief reaches can decrease the mean and variance of bed relief at least temporarily in general at both sites the degree of impact increased with the thickness of sediment delivered to the cross section results thus suggest that the analysis is a useful step for understanding the morphological effects of sediment pulses introduced to gravel bed bar pool channels copyright 2015 john wiley sons ltd

reply on eel river margin source to sink sediment budgets revisited by j a warrick marine geology 351 2014 25 37

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in beiya area western yunnan china abstract lamprophyres consisting mainly of diopside phlogopite and k feldspar formed in the early tertiary around 60 ma in the beiya area and are characterized by low sio 2 46 50 wt rb 31 45 ppm and sr 225 262 ppm high al 2 o 3 11 2 13 1 wt cao 8 0 8 7 wt mgo 11 5 12 1 wt k 2 o 4 9 5 5 wt tio 2 2 9 3 3 wt and ree 174 177 ppm and compatible elements e g sc cr and ni and hsf elements e g th u zr nb ta ti and y and low 143 nd 144 nd 0 512372 0 512536 middle 87 sr 86 sr 0 707322 0 707395 middle 206 pb 204 pb 18 50 18 59 207 pb 204 pb 15 60 15 65 and 208 pb 204 pb 38 75 38 8 these rocks developed peculiar quartz megacrysts with poly layer reaction zones melt inclusions and partial melted k feldspar and plagioclase inclusions and plastic shapes important features of these rocks include 1 hybrid composition of elements 2 abrupt increase of sio 2 content of the melt recorded by zoned diopside 3 development of sanidine and aegirine augite reaction zones 4 alkaline melt and partial melted k feldspar and plagioclase inclusions 5 deformed quartz inclusions associated with quartz megacrysts 6 the presence of quartz megacrysts in plastic shape with their parent melts 7 the occurrence of olivine high mgo ilmenite and spinel inclusions within earlier formed diopside phlogopite and magnetite median 87 sr 86 sr values between tertiary alkaline porphyries in the beiya area and the western yunnan and tertiary basalt in the western yunnan indicate that the beiya lamprophyre melts were derivative and resulted from the mixing between basic melts that were related to the partial melting of phenocrysts of spinel iherzolite from a mantle source the alkaline melts originated from partial melting along the jinshajiang subduction ductile shear zone at the contact between the buried palaeo tethyan oceanic lithosphere and the upper mantle lithosphere the alkaline melts are composed of 65 sanidine or 70 ab 28 an 2 and 35 sio 2 the melt mixing occurred in magma chambers in the middle shallow crust at 8 10 km before the derivative lamprophyre melts intruded into the shallow cover in beiya area this mixing of basic and alkaline melts might represent a general process for the formation of lamprophyre in the western yunnan

the bed morphology of upland single thread channels in semi arid environments evidence of repeating bedforms and their wider implications for gravel bed rivers single thread gravel bed streams of moderate slope in the northern negev are characterized by three channel units bars exhibit steeper than average slopes and poorly sorted mixtures of small medium cobbles and coarse very coarse pebbles flats are associated with more gentle slopes and well sorted medium fine pebbles and granules and transitional units have intermediate slopes and grain size in general all three units are planar span the full channel width and have well defined boundaries bars and flats are more common than the transitional units and alternate downstream for distances of several hundred metres forming sequences that are reminiscent of the riffle pool structure commonly observed in humid temperate gravel bed rivers a notable contrast is the absence of significant bed relief bars lack crests and flats lack depressions the relative lack of bed relief in bar flat sequences is attributed to the high rate of sediment supply from the sparsely vegetated hillslopes which promotes the infilling of depressions and to the erosion of crests under conditions of intense transport this reduction of bed relief lowers channel roughness which in turn increases flow velocity and therefore the ability of the channel to transmit the large sediment loads it receives although our analyses pertain to a semi arid river system the results have wider implications for understanding the adjustment of channel bedform to high sediment loads in other fluvial environments copyright 2012 john wiley sons ltd

altered regional sediment transport regime after a large typhoon southern taiwan analyses of river suspended sediment response to record breaking regional rainfall in southern taiwan during typhoon morakot 7 9 august 2009 reveal systematic changes in the regional sediment transport regime as characterized by rating curve parameters with decreasing b typically considered to be a constant for a given gauging station and increasing intercept k values in concentration discharge c q relations c kq b these changes result in much greater sediment concentration and thus sediment transport in subsequent low flow events after the typhoon an effect that amplifies and extends the influence of such extreme events through increased low flow sediment transport our finding that the exponent b is not constant contrasts with the conventional assumption that large events influence sediment yields through increased intercept k values thereby supporting the interpretation that basin sediment delivery influences both rating parameters and increases post event low flow sediment transport surveys of landslide density and riverbed grain sizes before and after typhoon morakot support the interpretation that the observed decrease in b values and the synchronous shift from an inverse correlation between k and mean catchment slope before the typhoon to a positive correlation afterward reflect an altered sediment transport regime and a change from channel migration and bank erosion to reworking of landslide debris and enhanced bed mobility as the dominant processes supplying fluvial sediment

rapid exhumation and cooling of the liaonan metamorphic core complex inferences from 40ar 39ar thermochronology and implications for late mesozoic extension in the eastern north china craton the liaonan metamorphic core complex formed during crustal extension in the liaodong peninsula eastern north china craton and consists of the jinzhou detachment fault proterozoic paleozoic sedimentary rocks in its upper plate and exhumed high grade archean metamorphic rocks and early cretaceous granitic plutons in the lower plate exhumation of its footwall from mid crustal levels is evidenced in the detachment fault zone by the temporal transition from amphibolite facies mylonitization at depth through retrograde chloritic shearing and brecciation to brittle faulting during final uplift the footwall mylonite zone is 2 5 3 5 km thick and includes early cretaceous 128 118 ma granitic rocks together with older metamorphic rocks the 40ar 39ar ages of muscovite hornblende biotite and k feldspar from the mylonitic rocks record that the core complex cooled between ca 120 and 107 ma from the time of initial crystallization of zircons 122 118 ma at 700 800 c in syntectonic leucocratic dikes and granitic rocks to closure of argon diffusion in hornblende micas and k feldspar at 500 to 200 c throughout the eastern north china craton the synchroneity of cooling and exhumation of metamorphic core complexes the formation of pull apart basins and regional alkaline igneous activity reflects regional extensional tectonics in the early cretaceous this accompanied lithospheric thinning possibly resulting from the rollback of the subducted pacific plate along the eastern asian margin during the early cretaceous

tectonic and economic implications of trace element 40ar 39ar and sm nd data from mafic dykes associated with orogenic gold mineralisation in central victoria australia abstract mafic to intermediate dykes are spatially and temporally closely associated with major post tectonic granitic complexes in the western lachlan orogen of se australia these dykes which range petrographically from basaltic to andesitic are concentrated within several north to northwest trending zones and were emplaced during two broad intervals of extensive magmatic activity during the silurian devonian period geochemical and sm nd isotopic characteristics of these mafic intrusives are consistent with their formation in a complex subduction related tectonic setting interaction between mantle wedge material sinking oceanic crust and input from the overlying continental crust resulted in the petrological and geochemical variations displayed by these and more felsic dykes throughout the study region field evidence and 40 ar 39 ar data show that in the eastern part of the stawell zone and in the northwest portion of the bendigo zone mafic dyke were intruded between 410 and 400 ma late silurian early devonian further emplacement in the bendigo zone and the eastern part of the melbourne zone took place at between 375 and 365 ma middle to late devonian episodic mantle derived magmatism was possibly related to step wise rollback slab detachment or changes in the angle and rate of westward subduction in response to periodically occurring accretionary pulses a close spatial and temporal relationship also exists between the dykes and orogenic gold mineralisation in the central victorian gold province mafic to intermediate dykes both crosscut and are host to mineralisation in a number of goldfields although there is little evidence for a direct genetic association the two processes are linked by the common utilisation of translithospheric structures which facilitated the rapid ascent into shallow crustal levels of both mantle derived magma and crustal scale ore forming fluid systems previous studies have suggested that transfer of heat into the crust via ascending mafic mantle magmas can provide a thermal engine which triggers and sustains extensive crustal melting thus explaining the commonly observed close association of mafic to intermediate and felsic intrusive suites this study supports the viability of this mechanism and in addition indicates that a causal link exists between the formation of mantle magmas in collisional zones and the generation of orogenic gold deposits

multiple sources for the origin of granites geochemical and nd sr isotopic evidence from the gudaoling granite and its mafic enclaves northeast china geochemical and sr and nd isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china the rocks include monzogranite porphyric granodiorite and quartz diorite monzogranites have relatively high 87rb 86sr ratios 0 672 0 853 low initial 87sr 86sr ratios 0 7052 0 7086 and e nd t values 18 5 to 20 9 indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time quartz diorites have high initial 87sr 86sr ratios 0 7118 0 7120 and negative e nd t values 13 2 to 18 1 coupled with high al2o3 and mgo contents indicating they were derived from enriched lithospheric mantle with contributions of radiogenic sr from plagioclase rich metagreywackes or meta igneous rocks i e ancient lower crust two groups of enclaves with igneous textures and abundant acicular apatites are distinguished dioritic enclaves and biotite monzonitic enclaves dioritic enclaves have low al2o3 13 5 16 4 wt and high mgo mg 72 3 concentrations low initial 87sr 86sr ratios 0 7058 0 7073 and negative e nd t values 7 2 and are enriched in liles and lrees and depleted in hfses suggesting they were derived from an enriched lithospheric mantle source biotite monzonitic enclaves have sr and nd isotopic compositions similar to the monzogranites indicating they were crystal cumulates of the parental magmas of these monzogranites granodiorites have transitional geochemistry and nd and sr isotopic compositions intermediate between the monzogranites quartz diorites and the enclaves geochemical and sr and nd isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mafic mantle derived and juvenile crustal derived magmas coupled with crystal fractionation and assimilation of ancient lower crust is compatible with the data this example shows that at least some calc alkaline granitoids are not produced by pure intracrustal melting but formed through a complex multi stage hybridization process involving mantle and crustal derived magmas and several concomitant magmatic processes crystal fractionation crustal assimilation and crustal anatexis

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

a hybrid origin for the qianshan a type granite northeast china geochemical and sr nd hf isotopic evidence abstract major and trace element whole rock sr and nd isotope and zircon hf isotope data are reported for a suite of a type granites and mafic microgranular enclaves from the early cretaceous 126 2 ma qianshan pluton liaodong peninsula northeast china with the aim of investigating the sources and petrogenesis of a type granites the qianshan pluton includes hornblende alkali feldspar granite graphic biotite granite and mafic microgranular enclaves the hornblende alkali feldspar granites have high sio 2 fe 2 o 3t mgo k 2 o na 2 o rb zr and lree contents and low ba and sr concentrations with strongly negative eu anomalies their high rb sr 87 rb 86 sr 16 76 24 15 and initial 87 sr 86 sr ratios 0 7215 to 0 7283 negative e nd t values 14 1 to 16 5 and zircon e hf t values 18 9 to 11 5 indicate they were mainly derived from a crustal source but with involvement of high e nd t and e hf t materials graphic biotite granites have similar geochemical features and sr nd hf isotopic compositions to enclaves indicating they were the result of crystal fractionation of evolved mafic magmas but with involvement of low e nd t and e hf t materials the mafic enclaves have an igneous texture and contain acicular apatite suggesting quenching of mafic magmas that have co mingled with the host granites they have low initial 87 sr 86 sr ratios 0 7097 0 7148 negative e nd t 14 5 to 11 9 and zircon e hf t 17 1 to 6 9 values and are enriched in liles and lrees and depleted in hfses when coupled with the high mgo mg up to 54 this indicates derivation from an enriched lithospheric mantle source but contaminated by crustal materials geochemical and sr nd and zircon hf isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mantle derived mafic and crustal derived magmas coupled with crystal fractionation is compatible with the data this example shows that at least some a type granites formed through a complex process involving mantle and crustal derived magma mixing crystal fractionation and infracrustal melting

temporal and spatial variability in thalweg profiles of a gravel bed river this study used successive longitudinal thalweg profiles in gravel bed rivers to monitor changes in bed topography followingfloodsandassociatedlargesedimentinputs variationsinchannelbedelevations distributionsofresidualwater depths percentage of channellengthoccupied byriffles andaspatial autocorrelationcoefficient moran si wereused to quantify changes in morphological diversity and spatial structure in redwood creek basin northwestern california bed topographyinredwoodcreekanditsmajortributariesconsistsprimarilyofaseriesofpoolsandriffles thesize frequency and spatial distribution of the pools and riffles have changed significantly during the past 20 years following large floods and highsediment input inredwood creek and its tributaries in 1975 variation in channelbed elevations was low and the percentageofthechannellengthoccupiedbyriffleswashigh overthenext20years variationinbedelevationsincreased while the length of channel occupied by riffles decreased an index standard deviation of residual water depth bankfull depth 100 wasdevelopedtocomparevariationsinbedelevationoverarangeofstreamsizes withahigherindexbeing indicativeofgreatermorphologicaldiversity spatialautocorrelationinthebedelevationdatawasapparentatbothfineand coarsescalesinmanyofthethalwegprofilesandtheobservedspatialpatternofbedelevationswasfoundtoberelatedtothe dominant channel material and the time since disturbance river reaches in which forced pools dominated and in which large woody debris and bed particles could not be easily mobilized exhibited a random distribution of bed elevations in contrast in reaches where alternate bars dominated and both wood and gravel were readily transported regularly spaced bed topography developed at a spacing that increased with time since disturbance this pattern of regularly spaced bed featureswasreversedfollowinga12 yearfloodwhenbedelevationsbecamemorerandomlyarranged copyright 1999 john wiley sons ltd

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

magma mixing in late archean tonalitic and mafic rocks of the lac des iles area western superior province abstract plutonic rocks in the lac des iles area of the western superior province provide a record of contemporaneous late archean mafic and tonalitic magmatism this suite of rocks consists of mafic to ultramafic intrusions mafic to intermediate dikes hornblendite and hornblende tonalite the tonalite contains net veined and disaggregated mafic to intermediate dikes mafic schlieren and zones of hornblendite to mela tonalite with skeletal hornblende these textures are interpreted to be the result of magma mixing the hornblende tonalite is geochemically characterized by high al 2 o 3 high na 2 o k 2 o low rb moderate sr and fractionated ree the hornblendite mafic to intermediate dikes and tonalite show whole rock trends of decreasing total ree increasing depletion of hree and increasing eu eu with increasing sio 2 amphiboles range in composition from edenitic and pargasitic hornblende to hornblende in dike rocks mela tonalite and hornblendite and from hornblende to actinolite in tonalite the development of skeletal amphiboles with strong normal zoning and resorbed hornblende with weak reverse zoning are attributed to conditions of supercooling and superheating respectively in zones of magma mixing the least fractionated dike rocks geochemically resemble lamprophyres derived from alkali basaltic magma variation of ree among the mafic to intermediate dikes suggests that they fractionated hornblende hornblendites and mela tonalites can be modeled as hornblende cumulates from the dike rocks the amphiboles probably crystallized rapidly during mixing leaving a feldspathic residue variation in hornblende tonalites is consistent with mixing of sio 2 rich tonalite melt with mafic to intermediate dike phases and associated hornblende cumulates and feldspathic residue open system magmatic processes at lac des iles result in a continuum of disequilibrium textures reflecting emplacement of mafic magma into a crystallizing felsic host the plutonic rocks probably formed from a zoned magma chamber with a mafic base and tonalitic top breccia zones in the tonalite suggest that explosive degassing of the chamber occurred structures similar to those reported here are common in other granitoids in the superior province and suggest that mafic magmatism and magma mixing played an important role in the development of late archean granitoid plutons

sediment transport storage relations for degrading gravel bed channels 1 in a drainage network sediment is transferred through a series of channel valley segments natural sediment storage reservoirs that are distinguished from their neighbors by their particular capacity to store and transport sediment we propose that the sediment transport capacity of each reservoir is a unique positive function of storage volume which influences sediment mobility and availability through variations in bed surface texture channel gradient and availability of valley floor sediments for erosion examinations of the form of transport storage relations of degrading alluvial reservoirs using published field studies flume experiments and simulations support a conceptual model that includes two phases in phase i filled channels respond to variations in supply primarily by changes in stored sediment volume with little change in transport rate in phase ii channel mobility is responsive to supply through armoring and form roughness although these phases could represent idealized transport limited phase 1 or supply limited phase ii states we propose that every alluvial reservoir responds to changes in sediment inputs by changing both storage and transport rate the propensity for either depending on reservoir characteristics and the sediment exchange processes in the channel transport storage relations for phase ii are approximately linear but examination of numerical simulations and flume experiments indicates that armoring imparts positive curvature simulations of degradation of an alluvial reservoir with channel and valley floor surfaces indicate that interactions between channel lowering and lateral erosion are critical in the manifestation of a transport storage relation better knowledge of transport storage relations could lead to improved sediment routing models for drainage basins wherein component sediment reservoirs dynamically adjust to varying sediment loads

controls on pool characteristics along a resistant boundary channel abstract the north fork poudre river in phantom canyon has a pool riffle sequence formed in granitic bedrock we address two questions what controls downstream pool spacing within a pool what factors control pool dimensions we hypothesize that both pool spacing and pool geometry could be governed by available flow energy or by substrate characteristics these hypotheses were addressed using channel bed and water surface gradients surveyed under moderate flow selby rock mass strength at vertical outcrops forming lateral pool constrictions and at other vertical outcrops and joint density measured from high resolution digital images of the bedrock outcrop along each of 10 pools the downstream length between pools is quite variable documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fonten

the influence of lee sediment behind large bed elements on bedload transport rates in supply limited channels a coarse surface layer can help to limit bedload transport rates in channels with cobble and gravel beds in these systems periodic boulder sized clasts often exist with small deposits of fine material in the lee of these large bed elements a combined field and flume study was conducted to investigate the potential impact of lee deposits with distinctly finer sediment sizes behind boulders on bedload transport rates detailed sediment characterizations were performed on surface subsurface and lee sediments in two coarse bedded connecticut channels bedload measurements also were conducted in a series of flows that approached the bankfull level in these two systems to determine transport rates and the size distribution of bedload material a 6 m long 0 5 m wide flume was used to model these systems with fine sediment passing over a fixed bed of sediment particles with uniform sized large bed elements sediment distributions of the lee deposits in the two connecticut channels indicate that lee deposits may be produced from winnowing of sediments from the surface layer lee deposits also exhibit sediment distributions similar to bedload sediment distributions from low to near bankfull flow in one of the two channels bedload sediments in the second channel were finer than lee deposits presumably from selective entrainment of fines flume experiments demonstrate that bedload transport rates are lower for periods of steady flow relative to periods that include either an increase or decrease in discharge the results show that lee sediments establish a metastable deposit behind each obstruction for a given discharge either increases or decreases in discharge disrupt this temporary stability and increase sediment delivery to the main flow the study suggests that the influence of the rate of change in discharge may be as important as the absolute magnitude of discharge on sediment transport rates at moderate and low discharges in sediment limited systems with large bed elements

geochronology of the pengjiakuang and rushan gold deposits eastern jiaodong gold province northeastern china implications for regional mineralization and geodynamic setting the jiaodong gold province the largest gold producing district in china is located in the jiaodong peninsula at the eastern margin of the north china craton and bounded by the continental scale tan lu fault 40 kin to the west previous geochronological studies suggest that pervasive gold deposition took place in the western part of the province between 122 and 119 ma here we report high quality ar 40 ar 39 ages of the pengjiakuang and rushan deposits from the eastern part of the jiaodong gold province placing additional chronological constraints on the timing of regional mineralization seven sericite grains extracted from auriferous alteration assemblages at the pengiiakuang deposit yielded well defined plateau ages between 120 9 0 4 and 119 1 0 2 ma 2 sigma three separates of igneous biotite from a sample of the queshan gneissic granite adjacent to the pengjiakuang deposit gave reproducible plateau ages of 124 6 0 6 to 123 9 0 4 ma 2 sigma six sericite separates front two samples in the rushan deposit yielded ar 40 ar 39 plateau ages at 109 3 0 3 to 107 7 0 5 ma 2 sigma whereas biotite from the kunyushan monzogranite that hosts the rushan deposit had plateau ages ranging from 129 0 0 6 to 126 9 0 6 ma 3 separates front one sample the apparent age gap between hydrothermal sericite and magmtic biotite from both deposits together with the similar argon closure temperatures for these mica minerals suggest that gold mineralization had no direct relationship to the granitoid magmatism instead gold deposition coincided with the emplacement of mafic to intermediate dikes widespread in the jiaodong gold province which have been dated at ca 122 to 119 ma and less commonly at 110 to 102 ma the new ar 40 ar 39 ages from the eastern jiaodong peninsula when combined with published data from the western part suggest that gold mineralization was broadly contemporaneous throughout the district the early cretaceous gold mineralization also is widely developed in four other major gold districts along the tan lu fault the temporal and spatial correlation of these gold deposits with mafic to intermediate dikes commonly found in most mineralized areas the presence of well documented metamorphic core complexes and half graben basins along the tan lu fault and voluminous basalts therein suggest that the early cretaceous was an important period of lithospheric extension possibly caused by the late mesozoic lithospheric thinning beneath the eastern block of the north china craton lithospheric thinning and extension could have resulted in abnormally high heat and fluid fluxes necessary for large scaled gold mineralization

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

stochastic forcing of sediment supply to channel networks from landsliding and debris flow sediment influx to channel networks is stochastically driven by rainstorms and other perturbations which are discrete in time and space and which occur on a landscape with its own spatial variability in topography colluvium properties and state of recovery from previous disturbances the resulting stochastic field of sediment supply interacts with the topology of the channel network and with transport processes to generate spatial and temporal patterns of flux and storage that characterize the sedimentation regime of a drainage basin the regime varies systematically with basin area we describe how the stochastic sediment supply is generated by climatic topographic geotechnical and biotic controls that vary between regions the general principle is illustrated through application to a landscape where sediment is supplied by mass wasting and the forcing variables are deterministic thickening of colluvium random sequences of root destroying wildfires and random sequences of rainstorms that trigger failure in a population of landslide source areas with spatial variance in topography and colluvium strength landslides stop in channels or convert to scouring debris flows depending on the nature of the low order channel network sediment accumulates within these channels for centuries before being transferred downstream by debris flows time series of sediment supply transport and storage vary with basin scale for any combination of climatic topographic and geotechnical controls in a companion paper benda and dunne this issue we use simulations of timing volumes and locations of mass wasting to study the interaction between a stochastically forced sediment supply and systematic changes of storage and flux through channel networks

landslides control the spatial and temporal variation of channel width in southern taiwan implications for landscape evolution and cascading hazards in steep tectonically active landscapes

the floating astronomical time scale for the terrestrial late cretaceous qingshankou formation from the songliao basin of northeast china and its stratigraphic and paleoclimate implications abstract the upper cretaceous qingshankou formation k 2 qn in the songliao basin slb of northeast china consists of up to 550 m thick lacustrine mudstone and shale that constitute one of the most important source rocks of the daqing oil field a high resolution cyclostratigraphic analysis of the natural gamma ray logging from 10 wells of the qingshankou formation k 2 qn reveals orbital cycles of precession 20 ka obliquity 40 ka and eccentricity 100 ka and 405 ka providing strong evidence for astronomically driven climate changes in the late cretaceous terrestrial environments floating astronomical time scales ats are established for all sections which demonstrate variable durations of k 2 qn across the basin 1 09 ma 5 20 ma and strong diachroneity of the lacustrine strata four periods of high depositional rates can be identified in the central parts of the basin possibly recording deposition during times of sustained wet climate and high chemical weathering an ats established from well m206 in the central depression zone of the basin where the most complete and stable milankovitch cycles are present suggests that the maximum duration of the k 2 qn is 5 20 ma from 94 27 ma to 89 07 ma late cenomanian to early coniacian the lacustrine anoxic event 1 lae1 at the cenomanian turonian boundary lasted 210 310 ka during which the most prolific petroleum source rocks in slb were deposited the onset 94 21 94 18 ma and duration 210 310 ka of lae1 in slb are comparable to those of the oceanic anoxic event 2 oae2 onset at 94 21 ma and duration of 320 900 ka suggesting that the same trigger mechanism such as increased atmospheric co 2 from large scale igneous activity may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems

geometric adjustment of pools to changes in slope and discharge a flume experiment abstract to characterize the factors controlling pool shape 30 different forced pools were created utilizing a 50 triangular constriction in a 0 5 m wide 6 m long recirculating flume pools were scoured from an initial plane bed of sand with a d50 of 0 25 mm pool depth and length were measured and used as dependent variables in least squares multiple regression analyses discharge channel bed gradient and energy slope were the independent variables additional linear regression analyses were conducted with either pool depth or length and stream power results indicate that both pool depth and length are primarily a function of discharge channel bed and energy slopes are also significantly related to pool length but are not significantly related to pool depth stream power is significantly related to both pool depth and length but r2 values for pool depth versus discharge indicate stronger relations than those between pool depth and stream power observations on the type of geometric adjustment indicate that pools may minimize their rate of energy expenditure primarily through elongation in contrast pool depth appears to be more sensitive to the characteristics of the constrictions that create the forced pools the results suggest that many field studies may suffer from cross correlation problems in particular channel erodibility may exert a more dominant influence on pool geometry than hydraulic controls in many constriction influenced channels

early yellowstone hotspot magmatism and gold metallogeny abstract high grade epithermal gold deposits in the northern great basin have long been associated with regional miocene basaltic to rhyolitic volcanism previous models for the low sulfidation epithermal gold ores in this region have generally portrayed the bimodal magmas as a source of heat to drive large scale convection of meteoritic water that leached gold from crustal sources and deposited it in hydrothermal vein systems or required that the gold evolve from fractionated silicic magmas new data of the present study indicate a more direct genetic link to the plume related basaltic magmas of the region laser 40ar 39ar incremental heating plateau ages for single crystals of adularia from several of these low sulfidation epithermal gold deposits range from 16 6 ma to 15 5 ma adularia from the jumbo deposit yields three concordant plateau ages with a combined statistical result of 16 54 0 04 ma 95 confidence level mswd 0 23 plateau ages for adularia from other deposits in the region and from gold bearing veins in the owyhee mountains of southwestern idaho yield similar ages up to 16 5 ma however some veins are as young as ca 15 5 ma and the grain to grain ages for a given sample can vary by up to ca 0 5 ma observed variations in age among the adularia crystals of a given rock sample indicate varying amounts of extraneous argon and also loss of radiogenic 40ar among the population of grains for a particular sample the single crystal results are interpreted to indicate a 16 5 15 5 ma interval for formation of gold bearing adularia veins in the region the initiation and duration of this gold forming event appears contemporaneous within uncertainties with the basaltic volcanism at the steens mountain section and an ensuing one million year episode of basaltic volcanism from multiple centers in the region brueseke et al 2007 trace amounts of lead are alloyed with gold in the deposits studied the isotopic compositions of this lead are not compatible with regional crustal units that host the gold ores or the silicic igneous lithologies of the region but have the same lead isotopic composition as basalts of the earliest yellowstone plume represented by the earliest lavas of the columbia river basalt province the steens basalts and stonyford volcanic complex hanan et al 2008 we propose that the gold studied and its traces of alloyed lead were derived together from the mantle released from basaltic magma chambers of the province and carried by low density fluids into shallow geothermal systems during the earliest stages of yellowstone hotspot magmatism

continuity of the north qilian and north qinling orogenic belts central orogenic system of china evidence from newly discovered paleozoic adakitic rocks abstract adakitic intrusive rocks of 430 450 ma were discovered in the north qilian orogenic belt the western section of the central orogenic system cos in china these adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal ce pb nb u ti eu and nd sm ratios and radiogenically enriched 87sr 86sr i of 0 7053 0 7066 and end t of 0 9 to 1 7 while they are all characterized by low yb 65 and la yb n 13 7 ratios these adakitic rocks are classified into the low mgo ni cr and high mgo ni cr groups the low mgo samples were derived from partial melting of thickened lower crust whereas the high mgo samples were melts from delaminated lower crust which subsequently interacted with mantle peridotite upon ascent adakitic rocks from the adjacent north qinling orogenic belt also originated from thickened lower crust at 430 ma in addition the north qilian and north qinling orogenic belts both consist of lithological assemblages varying from subduction accretionary complexes at south to central arc assemblages which include adakitic rocks then to backarc phases at north such a sequence reflects northward subduction of the qilian and qinling oceans in these two orogenic belts the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern qilian and western qinling forming a 1000 km early paleozoic orogenic belt in such a tectonic configuration the qilian and qinling oceans that subducted from south possibly represent parts of the large proto tethyan ocean this inference is supported by the coexistence of early paleozoic coral and trilobite specimens from asia america and australia in the north qilian orogenic belt post 400 ma volcanic rocks occur in the north qinling orogenic belt but are absent in the north qilian orogenic belt indicating that these two orogenic belts underwent distinct evolution history after the closure of the proto tethyan ocean 420 ma

effects of three gorges dam operation on spatial distribution and evolution of channel thalweg in the yichang chenglingji reach of the middle yangtze river china abstract the evolution of the channel thalweg and pool riffle sequences is a critical feature of morphological adjustments in fluvial systems and might have important effects on aquatic habitat quality channel stability and navigation based on the 220 cross sectional profiles from 2002 to 2016 residual depths and spatial statistical analyses were used to quantitatively analyse the vertical variations and longitudinal distribution of the pool riffle sequences and channel thalweg in the yichang chenglingji reach ycr of the middle yangtze river which consists of the yizhi zhijiang shashi gongan and shishou jianli sub reaches the results showed that the dramatic reduction in the sediment loads following the construction of the three gorges dam tgd has caused significant adjustments in the size morphological diversity and spatial distribution of pool riffle structures in the ycr the average depth of the pools in the yizhi zhijiang reach and the shishou jianli reach overall exhibited a nonlinear growth trend with the average residual depth increasing by 1 4 m and 1 9 m respectively however the average residual depth in the shashi gongan reach showed a decreasing trend with a reduction of approximately 1 2 m the longitudinal lengths of the riffles in all three reaches contracted to different degrees and the specific percentage of longitudinal river length occupied by riffles total riffle length total sub reach length decreased by 8 9 6 and 5 9 in the three sub reaches from upstream to the downstream in addition the morphological diversity of the thalweg elevation in the shashi gongan reach and shishou jianli reach weakened after the construction of the tgd while the bed topography in the yizhi zhijiang reach became more complex and diverse moreover the pool riffle structures in the ycr were rearranged and distributed regularly following the initiation of the tgd operation although the variation characteristics of the average pool spacing in the three sub reaches were quite different quantitative relationship between the average residual depth and the previous four year hydrological condition was proposed for the three sub reaches based on the delayed response model drm and verified using the measurements from 2013 to 2016

the influence of relative sediment supply on riverine habitat heterogeneity abstract the diversity of aquatic habitats in streams is linked to physical processes that act at various spatial and temporal scales two components of many that contribute to creating habitat heterogeneity in streams are the interaction between sediment supply and transport capacity and the presence of local in stream structures such as large woody debris and boulders data from previously published flume and field studies and a new field study on tributaries to the south yuba river in nevada county california usa were used to evaluate the relationship between habitat heterogeneity local in stream structural features and relative sediment supply habitat heterogeneity was quantified using spatial heterogeneity measures from the field of landscape ecology relative sediment supply as expressed by the sediment supply transport capacity ratio which controls channel morphology and substrate textures two key physical habitat characteristics was quantified using a dimensionless bedload transport ratio q calculated q values were plotted against an ecologically meaningful heterogeneity index shannon s diversity index measured for each study reach as well as the percent area of in stream structural elements the results indicate two potential mechanisms for how relative sediment supply may drive geomorphic diversity in natural river systems at the reach scale when less mobile structural elements form a small proportion of the reach landscape the supply capacity ratio dictates the range of sediment textures and geomorphic features observed within the reach in these settings channels with a moderate relative sediment supply exhibit the highest textural and geomorphic diversity in contrast when less mobile structural elements are abundant forced local scour and deposition creates high habitat heterogeneity even in the presence of high relative sediment supply

temperature and bulk composition control on the growth of monazite and zircon during low pressure anatexis mount stafford central australia the formation age and trace element composition of zircon and monazite were investigated across the prograde low pressure metamorphic sequence at mount stafford central australia three pairs of inter layered metapelites and metapsammites were sampled in migmatites from amphibolite facies t 600 c to granulite facies conditions t 800 c sensitive high resolution ion microprobe u pb dating on metamorphic zircon rims and on monazite indicates that granulite facies metamorphism occurred between 1795 and 1805ma the intrusion of an associated granite was coeval with metamorphism at 1802 3ma and is unlikely to be the heat source for the prograde metamorphism metamorphic growth of zircon started at t 750 c well above the pelite solidus zircon is more abundant in the metapelites which experienced higher degrees of partial melting compared with the associated metapsammites in contrast monazite growth initiated under sub solidus prograde conditions at granulite facies conditions two distinct metamorphic domains were observed in monazite textural observations petrology and the trace element composition of monazite and garnet provide evidence that the first metamorphic monazite domain grew prior to garnet during prograde conditions and the second in equilibrium with garnet and zircon close to the metamorphic peak ages from sub solidus prograde and peak metamorphic monazite and zircon are not distinguishable within error indicating that heating took place in less than 20 myr

observations of event based streambed deformation in a gravel bed channel 1 the streambed is the major source of bed load sediment in gravel bed channels and is necessarily deformed during floods that mobilize sediment this study uses observations of scour and fill from carnation creek canada to articulate at a point relations of the occurrence and magnitude of bed deformation and the resulting adjustments in bed configuration over a series of flood events the likelihood of local bed deformation by scour fill or both depends on flow magnitude at most locations there is an imbalance of scour and fill that leads to adjustments in bed elevation and these imbalances increase with flow persistent deformation of locations in lower portions of the bed topography tend to produce larger total exchanges between bed and mobile sediment over the flood series but locations that experience similar frequencies of bed deformation do not produce unique depth distributions these results underscore the importance of understanding the coupling of scour and fill that produces streambed adjustment when modeling streambed evolution and managing river habitat

differential bed sedimentology and the maintenance of riffle pool sequences abstract riffle pools are the characteristic reach scale bedforms of gravel and mixed bedded channels of low to moderate slope the purpose of this paper is to clarify several aspects of the sedimentology of riffle pool sequences and to suggest how these both reflect and control riffle pool stability in the presence of spatial differences in the turbulent near bed flow field high frequency velocity measurements obtained using an array of electromagnetic current meters are combined with results from grid and transect sampling of bed sediments from 9 sites on 3 small upland rivers in n exmoor u k riffle sediments are shown to possess greater development of microtopographic structuring than adjacent pools which enhances riffle stability and which may reflect greater turbulent kinetic energy there over most of the flow range data on surface sediment arrangement and turbulent flow characteristics can be combined with different transport threshold equations to explain the maintenance of riffle pool sequences with respect to a particle queuing kinematic wave model without recourse to a competence reversal as conventionally assumed

an appraisal of the velocity reversal hypothesis for stable pool riffle sequences in the river severn england the velocity reversal hypothesis is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool riffle sequences in gravel bedded streams the literature in support of the hypothesis together with published adverse criticism is reviewed it is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow high stage and stable morphology these observations are substantiated by a detailed study of the hydraulic geometry of stable pool riffle sequences in the river severn england neither the sectionally averaged velocity nor the near bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases a detailed investigation of the three dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles the hydraulic data are used to comment on the stability of the test reaches in the context of the development of the river severn in the vicinity of shrewsbury

random controls on semi rhythmic spacing of pools and riffles in constriction dominated rivers average pool spacing between five and seven bankfull widths has been documented in environments throughout the world but has limited theoretical justification in coarse bedded and bedrock environments pool formation in coarse bedded and bedrock channels has been attributed to bedrock and boulder constrictions because the spacing of these constrictions may be irregular in nature it is difficult to reconcile pool formation processes with the supposedly rhythmic spacing of pools and riffles to address these issues a simulation model for pool and riffle formation is used to demonstrate that semi rhythmic spacing of pools with an approximate spacing of five to seven bankfull widths can be recreated from a random distribution of obstructions and minimum pool and riffle length criteria it is assumed that a pool riffle couplet will achieve a minimum length based on dominant discharge conditions values for the minimum length assumption are based on field data collected in new england and california while the theoretical basis relies on the demonstrated hydraulic response of individual pools to elongation results from the simulations show that the location of pools can be primarily random in character but still assume an average spacing between four and eight bankfull widths for a variety of conditions field verification data generally support the model but highlight a highly skewed distribution of pool forming elements and pool spacing the relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant discharge conditions copyright 2001 john wiley sons ltd

channel responses to varying sediment input a flume experiment modeled after redwood creek california article i nfo storage flume aggradation degradation at the reach scale a channel adjusts to sediment supply and flow through mutual interactions among channel form bed particle size and flow dynamics that govern river bed mobility sediment can impair the beneficial uses of a river but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing we use a flume experiment coupled with field measurements in a gravel bed river to explore sediment transport storage and mobility relations under various sediment supply conditions our flume experiment modeled adjustments of channel morphology slope and armoring in a gravel bed channel under moderate sediment increases channel bed elevation increased and sediment output increased but channel planform remained similar to pre feed conditions during the following degradational cycle most of the excess sediment was evacuated from the flume and the bed became armored under high sediment feed channel bed elevation increased the bed became smoother mid channel bars and bedload sheets formed and water surface slope increased concurrently output increased and became more poorly sorted during the last degradational cycle the channel became armored and channel incision ceased before all excess sediment was removed selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored our flume results of changes in bed elevation sediment storage channel morphology and bed texture parallel those from field surveys of redwood creek northern california which has exhibited channel bed degradation for 30 years following a large aggradation event in the 1970s the flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur but the channel may return to a state of balancing sediment supply and transport capacity published by elsevier b v

transport and storage of bed material in a gravel bed channel during episodes of aggradation and degradation a field and flume study the dynamics of sediment transport capacity in gravel bed rivers is critical to understanding the formation and preservation of fluvial landforms and formulating sediment routing models in drainage systems we examine transport storage relations during cycles of aggradation and degradation by augmenting observations of three events of channel aggradation and degradation in cuneo creek a steep 3 gravel bed channel in northern california with measurements from a series of flume runs modeling those events an armored single thread channel was formed before feed rates were increased in each aggradation run output rates increased as the channel became finer and later widened steepened and braided after feed rates were cut output rates remained high or increased in early stages of degradation as the incising channel remained fine grained and later decreased as armoring intensified if equilibrium was not reached before sediment feed rate was cut then a rapid transition from a braided channel to a single thread channel caused output rates for a given storage volume to be higher during degradation than during aggradation variations in channel morphology and surface bed texture during runs that modeled the three cycles of aggradation and degradation were similar to those observed in cuneo creek and provide confidence in interpretations of the history of change cuneo creek aggraded rapidly as it widened shallowed and braided then degraded rapidly before armoring stabilized the channel such morphology driven changes in transport capacity may explain the formation of flood terraces in proximal channels transport storage relations can be expected to vary between aggradation and degradation and be influenced by channel conditions at the onset of changes in sediment supply published in 2011 this article is a us government work and is in the public domain in the usa

response and recovery of the eel river california and its tributaries to floods in 1955 1964 and 1997 abstract northwestern california is prone to regional high magnitude winter rainstorms which repeatedly produce catastrophic floods in the basins of the northern coast ranges major floods on the eel river in 1955 and 1964 resulted in substantial geomorphic changes to the channel adjacent terraces and tributaries this study evaluated the changes and the effects of a moderate flood in 1997 through field observations and examination of aerial photographs that spanned from 1954 to 1996 the purpose was to document the nature and magnitude of geomorphic responses to these three floods and assess the rates and controls on the recovery of the eel river and its tributaries channel widening from extensive bank erosion was the dominant geomorphic change along the lower eel river during major floods as a result of the 1964 flood the largest amount of widening was 195 m and represented an 80 change in channel width channel narrowing characterized the periods after the 1955 and 1964 floods more than 30 years after the 1964 flood however the river had not returned to pre flood width which suggests that channel recovery required decades to complete a long recovery time is unusual given that the eel river is located in an area with a superhumid climate and has an exceptionally high sediment yield this long recovery time may reflect highly seasonal precipitation and runoff which are concentrated in 3 5 months each winter in contrast to the main stem of the eel river the dominant effects of floods on the tributaries of the eel river were rapid aggradation of channel bed and valley floor followed by immediate downcutting dendrogeomorphic data aerial photographs and field observations indicate that thick wedges of gravel derived largely from hillslope failures in upper reaches of the tributaries are deposited at and immediately upstream of the mouths of tributaries as the stage of the eel river exceeded that of the tributaries during major floods in the waning stages of the flood the tributaries cut through the gravel at a rate equal to the lowering of the eel and generated unpaired terraces and nickpoints the complete process of deposition and incision can occur within a few days of peak discharge although reworking of some sediment on the valley floor may continue for years after large floods channel morphology in the tributaries appears to be a product of infrequent high magnitude events the morphology of the tributary channel also appears to be greatly influenced by the frequency and magnitude of mass wasting in headwater areas of small basins

formation of wulong mafic dikes via mixing of enriched lithospheric mantle derived and crustal magmas eastern north china craton abstractzircon u pb age and geochemical data are reported for the wulong dike swarms from the liaodong peninsula ne china the studied dikes include diorite lamprophyre and dolerite together with previous dating the diverse rocks have a peak age of ca 120 125 ma they are marked by inversely zoned phenocrysts with mg and cr rich rims and they exhibit mantle like signatures i e high mg cr ni associated with prominent subduction type element enrichments the early diorites have relatively radiogenic sr 0 7143 and less radiogenic nd to 11 0 isotopes coupled with high and variable mgo cr ni contents indicating that they were mainly derived from ancient lower crust with subordinate contributions of enriched lithospheric mantle the transitional lamprophyres are characterized by high rb sr ratios 0 22 0 54 but low initial 87sr 86sr ratios 0 7069 0 7093 moderate negative end t values 14 4 to 12 6 and low promantle elements such as mg cr ni reflecting that juvenile lower crust

do lamprophyres carry gold as well as diamonds diamonds are now known from kimberlites lamproites and alkaline and ultramafic lamprophyres here we point out that these rocks are also significantly enriched in gold as are calc alkaline lamprophyres the average gold abundance in lamprophyres seems to be at least an order of magnitude higher than in common igneous rocks and many individual values are 100 1 000 times higher this high gold content may reflect two factors 1 lamprophyres tap exceptionally deep regions of the earth regions not only where diamond is stable but also where gold may be more enriched than in the source regions for other igneous rocks 2 lamprophyre magmas are suitable carriers of gold from depth because in their high co2 h2o f k rb and ba but moderate s contents they closely mirror fluids actually known to deposit gold veins in the crust most types of lamprophyre rise rapidly enough from great depths to retain any diamond and gold along with rich mantle xenolith suites calc alkaline lamprophyres on the other hand undergo extensive crustal interactions which cause them to pick up crustal xenoliths and to lose any diamond and mantle xenoliths along with at least some of their gold this last may account for their association with mesothermal for example archaean gold deposits

a roughness corrected index of relative bed stability for regional stream surveys abstract quantitative regional assessments of streambed sedimentation and its likely causes are hampered because field investigations typically lack the requisite sample size measurements or precision for sound geomorphic and statistical interpretation we adapted an index of relative bed stability rbs for data calculated from a national stream survey field protocol to enable general evaluation of bed stability and anthropogenic sedimentation in synoptic ecological surveys rbs is the ratio of bed surface geometric mean particle diameter dgm divided by estimated critical diameter dcbf at bankfull flow based on a modified shield s criterion for incipient motion application of rbs to adequately depict bed stability in complex natural streams however has been limited because typical calculations of rbs do not explicitly account for reductions in bed shear stress that result from channel form roughness we modified the index rbs to incorporate the reduction in bed shear stress available for sediment transport that results from the hydraulic resistance of large wood and longitudinal irregularities in channel dimensions form roughness based on dimensional analysis we derived an adjustment to bankfull shear stress by multiplying the bankfull hydraulic radius rbf by the one third power of the ratio of particle derived resistance to total hydraulic resistance cp ct 1 3 where both resistances are empirically based calculations we computed cp using a keulegan equation relating resistance to relative submergence of bed particles we then derived an empirical equation to predict reach scale hydraulic resistance ct from thalweg mean depth thalweg mean residual depth and large wood volume based on field dye transit studies in which total hydraulic resistance ct was measured over a wide range of natural stream channel complexity including manipulation of large wood volumes we tested our estimates of ct and rbs by applying them to data from a summer low flow probability sample of 104 wadeable stream reaches in the coastal ecoregion of oregon and washington usa stream discharges calculated using these ct estimates compared favorably with velocity area measurements of discharge during summer low flow and with the range of 1 to 2 year recurrence floods scaled by drainage area at u s geological survey gauged sites in the same region log rbs ranged from 4 2 to 0 98 in the survey region dgm ranged from silt to boulders while estimated bankfull critical diameter d cbf ranged from very fine gravel to large boulders the median value of d cbf adjusted for form roughness influences averaged 40 inter quartile range 28 to 59 of the unadjusted estimate dcbf log rbs was consistently negatively related to human disturbances likely to produce excess sediment inputs or hydrologic alteration log rbs ranged from 1 9 to 0 5 in the streams within the lower quartile of human disturbance in their basin and riparian areas and was substantially lower 4 2 to 1 1 in streams within the upper quartile of human disturbance the synoptic survey methods and designs we used appear adequate to evaluate regional patterns in bed stability and sedimentation and their general relationship to human disturbances although the rbs concept also shows promise for evaluating sediment and bed stability in individual streams our approach is relatively coarse so site specific assessments using these rapid field methods might prudently be confined to identifying severe cases of sedimentation or channel alteration greater confidence to discern subtle differences in site specific assessments could be gained by calculating rbs using more precise field measurements of channel slope bed particle size and bankfull dimensions and by refining our adjustments for energy loss from channel form roughness

petrogenesis of late triassic granitoids and their enclaves with implications for post collisional lithospheric thinning of the liaodong peninsula north china craton abstract major and trace element sr nd and hf isotope zircon u pb and hf isotope data are reported for mafic microgranular enclaves and host granitoids from the xiuyan pluton in the liaodong peninsula of the eastern north china craton in order to investigate their sources petrogenesis and tectonic implications the zircon u pb age of the enclaves 211 1 ma is identical to that of the host granite 210 1 ma establishing that the mafic and felsic magmas were coeval the enclaves have high mgo concentrations at low silica contents and positive ehf t values they are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements which can be explained as melts derived from a depleted asthenospheric mantle with some crustal contamination the host granitoids have high sio2 contents variable initial 87sr 86sr ratios and highly negative end t and ehf t values suggesting they were mainly derived from an ancient crustal source heated by the input of asthenospheric mantle derived magmas field observations geochronology geochemistry sr and nd isotopic and zircon hf isotopic compositions point to a complex petrogenesis where asthenospheric mantle and crust derived magma mixing was coupled with crystal fractionation thus explaining the genetic link between enclaves and host rocks identification of an asthenospheric mantle component in the xiuyan granitoids suggests asthenospheric mantle upwelling and decompressional melting of the mantle indicating that post collisional lithospheric thinning in the liaodong peninsula was initiated in the late triassic

the liaonan metamorphic core complex southeastern liaoning province north china a likely contributor to cretaceous rotation of eastern liaoning korea and contiguous areas abstract the mesozoic liaonan metamorphic core complex mcc of the southeastern liaoning province north china is an asymmetric cordilleran style complex with a west rooting master detachment fault the jinzhou fault a thick sequence of lower plate fault related mylonitic and gneissic rocks derived from archean and early cretaceous crystalline protoliths has been transported ese ward from mid crustal depths u pb ages of lower plate syntectonic plutons ca 130 120 ma 40 ar 39 ar cooling ages in the mylonitic and gneissic sequence ca 120 110 ma and a cretaceous supradetachment basin attest to the early cretaceous age of this extensional complex the recent discovery of the coeval and similarly west rooting waziyu mcc in western liaoning darby b j davis g a zhang x wu f wilde s yang j 2004 the newly discovered waziyu metamorphic core complex yiwulushan western liaoning province north china earth science frontiers 11 145 155 indicates that the gulf of liaoning which lies between the two complexes was the center of a region of major crustal extension clockwise crustal rotation of a large region including eastern liaoning province and the korean peninsula with respect to a non rotated north china block has been conclusively documented by paleomagnetic studies over the past decade the timing of this rotation and the reasons for it are controversial lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 proposed that a clockwise rotation of 22 5 10 2 was largely post early cretaceous in age and was the consequence of extension within a crustal domain that tapers southwards towards the bohai sea of which the gulf of liaoning is the northernmost part paleomagnetic studies of early cretaceous strata ca 134 120 ma in the yixian fuxin supradetachment basin of the waziyu mcc indicate the non rotation of north china and the basin zhu r x shao j a pan y x shi r p shi g h li d m 2002 paleomagnetic data from early cretaceous volcanic rocks of west liaoning evidence for intracontinental rotation chinese science bulletin 47 1832 1837 such upper plate non rotation supports our conclusion that the lower plates of the waziyu and liaonan metamorphic core complexes were displaced ese ward in an absolute sense away from the stable north china block thus contributing to the rotation of korea and contiguous areas rotation is inferred to have affected only the upper crust above mid crustal levels into which we believe the jinzhou and waziyu detachment fault zones flattened if this is the case the regional tan lu fault that lies between the two core complexes was truncated at mid crustal depth since in areas to the south it forms the boundary between the north and south china lithospheric blocks it is noteworthy that the two extensional complexes lie not far north of the bohai bay the area proposed by lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 as the site of the pole of rotation for korea s clockwise displacement lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 were unaware of the liaonan and waziyu mcc s and argued that most of the regional block rotation was post early cretaceous and in part early cenozoic however the ca 130 120 ma ages of the two liaoning mcc s and a songliao basin mcc xujiaweizi the latter discovered only by recent drilling through its younger stratigraphic cover support our and some korean coworkers conclusions that most of the clockwise rotation was early cretaceous

the influence of pool length on local turbulence production and energy slope a flume experiment the in uence of pool length on the strength of turbulence generated by vortex shedding was investigated in a 6 m long recirculating ume the experiment utilized a 38 constriction of ow and an average channel bed slope of 0 007 the base geometry for the intermediate length pool experiment originated from a highly simpli ed 0 10 scale model of a forced pool from north saint vrain creek colorado discharge in the ume was 31 6 l s which corresponds to a discharge in the prototype channel of 10 m3 s three shorter and four longer pool lengths also were created with a xed bed to determine changes in turbulence intensities and energy slope with pool elongation three dimensional velocities were measured with an acoustic doppler velocimeter at 31 40 different 0 6 depth and near bed locations downstream of the rectangular constriction the average velocity and root mean square rms of the absolute magnitude of velocity at both depths are signi cantly related to the distance from the constriction in most pool locations downstream of the constriction in many locations pool elongation results in a non linear change in turbulence intensities and average velocity based on the overall ow pattern the strongest turbulence occurs in the center of the pool along the shear zone between the jet and recirculating eddy the lateral location of this shear zone is sensitive to changes in pool length energy slope also was sensitive to pool length due to a combination of greater length of the pool and greater head loss with shorter pools the results indicate some form of hydraulic optimization is possible with pools adjusting their length to adjust the location and strength of turbulent intensities in the center of pools and lower their rate of energy dissipation copyright 2004 john wiley sons ltd

identifying dynamic equilibrium of an undeveloped alluvial stream by extremal hypotheses abstract the indeterminate channel problem arises from uncertainty in finding a closure relation for alluvial channels created by self organizing erosional and depositional processes extremal hypotheses have been proposed as one potential approach to closing the system of governing equations for alluvial channels many different extremal hypotheses have been presented but no substantive evidence has been developed to select which hypothesis may be most appropriate for natural alluvial river systems this paper evaluates the ability of ten extremal hypotheses to identify dynamic equilibrium across a geomorphic gradient in the remote and undeveloped mid latitude watershed of rio murta chile this study a introduces extremal hypotheses b describes the field site and geomorphic conditions and c examines which extremal hypotheses are supported by the field data in identifying the evolutionary trend toward dynamic equilibrium the extremal hypotheses that identified dynamic equilibrium within the geomorphic gradient in the field are 1 minimum kinetic energy 2 minimum specific stream power 3 maximum friction factor and 4 maximum total friction factor which collectively support minimizing kinetic energy of the system

fine bed material in pools of natural gravel bed channels natural gravel bed channels commonly contain a fine mode of sand and fine gravel that fills voids of the bed framework of coarser gravel if the supply of fine bed material exceeds the storage capacity of framework voids excess fine material forms surficial patches which can be voluminous in pools during low flow data collected in 34 natural channels in northern california and southern oregon indicate the following 1 fine material on the bed surface can be readily winnowed and transported at high particle velocities much of it in intermittent suspension fine material can dominate the bed material load in gravel bed channels but its abundance on the bed surface is limited by its increasing mobility as hiding places among prominent particles are filled 2 fine material in pools is typically replaced many times per year 3 the proportion v of residual pool volume filled with fine bed material correlates with annual sediment yield in channels whose parent material produces abundant sandy sediment 4 temporal and spatial changes in v appear to correspond to variations in the balance between sediment inputs and water discharge these results suggest that v can be used to monitor and evaluate the supply of excess fine material in gravel bed channels and that samples of fine material in pools can characterize the fine mobile mode of bed material load the sediment load of a stream channel the amount supplied and transported over a period of time can be difficult to evaluate contributions from hillslopes can be quantified with erosion surveys and sediment budgeting but uncertainty in routing makes it difficult to assess the load at any point in a channel network and direct measurement of transport rates is notoriously difficult bed material typically furnishes the bulk of the annual bed load especially in more distal channels but the active volume that contributes to the load is highly variable and difficult to evaluate it may be easier to detect variations in load by examining the mobility of the bed surface of gravel bed channels bed material in gravel bed channels characteristically includes a wide range of particle size and the bed can become

effects of aggradation and degradation on riffle pool morphology in natural gravel channels northwestern california after the flood of december 1964 12 gaging sections in northern california widened as much as 100 and aggraded as much as 4 m and then degraded to stable levels during a period of 5 years or more as channels aggraded bed material became finer and low to moderate flow through gaging sections in pools became shallower faster and steeper comparisons of longitudinal profiles also show the diminishment of pools as well as a decrease in bar relief accompanying the excessive sediment load as gaging sections degraded hydraulic geometries recovered to a limited degree full recovery probably depends on channel narrowing and further depletion of sediment supply the hydraulic changes with aggradation indicate an increase in the effectiveness of moderate discharges less than i to 2 year recurrence interval annual flood series to transport bed load and shape the bed bars become smaller pools preferentially fill and rimes armored with relatively small gravel tend to erode headward during falling stages and form a gentler gradient excess sediment can thus be more readily transported out of channels when additional contributions from watersheds are usuall slight

late paleozoic calc alkaline to shoshonitic magmatism and its geodynamic implications yuximolegai area western tianshan xinjiang article i nfo continuous late paleozoic magmatic activity in the western tianshan xinjiang china temporally overlapped the late carboniferous collision between the tarim and the kazakhstan yili plates isotopic dating whole rock geochemistry and isotopic characteristics of a suite of calc alkaline to shoshonitic rocks from yuximo legai area in the eastern end of the awulale mountains help define the tectonic evolution of this part of the tianshan zircon u pb ages of a quartz diorite and a quartz syenite porphyry are 310 8 2 1 ma and 284 4 3 6 ma respectively the geochemical and isotopic characteristics of late carboniferous igneous rocks including the quartz diorite as well as basaltic andesite and k rich trachyandesite indicate an evolu tion from calc alkaline towards shoshonitic series this was generated by the partial melting of the hydrated mantle wedge induced by changing subduction angles the younger quartz syenite porphyry however was more likely derived from the partial melting of a thickened crust in a post collisional setting or the partial melting of hot juvenile basalt in the lower crust during early permian delamination of the subcontinental lithospheric mantle therefore the generation of the calc alkaline to shoshonitic igneous rocks in yuximole gai area is genetically linked to the geodynamic evolution of the western tianshan from convergent subduc tion to collision during the late paleozoic

eel river margin source to sink sediment budgets revisited abstract the eel river coastal margin has been used as a representative source to sink sediment dispersal system owing to its steep high sediment yield river and the formation of sedimentary strata on its continental shelf one finding of previous studies is that the adjacent continental shelf retains only 25 of the eel river fine grained sediment less than 63 m discharged over time scales of both individual floods and the 20th century thus suggesting that the eel shelf trapping efficiency is uniquely lower than other similar systems here i provide data and analyses showing that sediment discharge relationships in the eel river have varied strongly with time and include substantial decreases in suspended sediment concentrations during the latter 20th century including these trends in margin wide sediment budgets i show that previous eel river sediment discharge rates were overestimated by a factor of two thus revised sediment budgets shown here reveal that the eel shelf retained 50 of the discharged river fine grained suspended sediment during intensively sampled events of 1995 97 and over the 20th century in light of this hypotheses about high rates of sediment export away from the primary shelf depocenter should be reevaluated

3800 to 2500 ma crustal evolution in the anshan area of liaoning province northeastern china shrimp u pb zircon geochronology has revealed several generations of granitoids and gneisses from the anshan area of northeastern china two samples of the baijiafen granite sensu lato 3804 5 and 3812 4 ma chentaigou granite 3306 13 ma lishan granite 3142 7 ma east and west anshan granites 3001 4 and 2994 8 ma tiejiashan granite 2962 4 and 2964 6 ma and qidashan granite 2475 ma the 3800 ma baijiafen granite consists of banded migmatitic trondhjemitic gneisses and forms only a small part of the area nonetheless they are the oldest known rocks in asia and are one of very few locations in the world where rocks of this antiquity have been found the younger suites are predominantly granite sensu stricto in composition and although foliated they have not been transformed into banded gneisses nd isotopic data suggest that the 3800 ma granites were produced at least in part by remelting of very ancient lree enriched sources perhaps like the exposed remnants of the 3800 ma rocks the chentaigou supracrustals contain layered mafic and ultramafic rocks banded iron formation bif and siliceous layered rocks of probable volcanogenic origin a sample of the latter has yielded a concordant u pb zircon age of 3362 5 ma interpreted as the age of deposition a trondhjemitic sheet cutting these rocks has yielded a u pb zircon age of 3342 6 ma the chentaigou supracrustals are the oldest recognised in the area younger supracrustal sequences collectively known as the anshan group contains the main economic bif units in the area bif is intruded by the 2475 ma qidashan granite indicating that the anshan group is archaean or earliest proterozoic in age

stochastic forcing of sediment routing and storage in channel networks the stochastic field of sediment supply to the channel network of a drainage basin depends on the large scale interactions among climatically driven processes such as forest fire and rainstorms topography channel network topology and basin scale during infrequent periods of intense erosion large volumes of colluvium are concentrated in parts of a channel network particularly near tributary junctions the rivers carry bed material and wash load downstream from these storage sites at different rates the bed material travels slowly creating transient patterns of sediment transport sediment storage and channel morphology along the channel network as the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion interference at tributary junctions and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion which converts bed material to wash load we investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215 km 2 drainage basin within the oregon coast range over a simulated 3000 year period with a climate typical of the late holocene we used field measurements and a simulation model to illustrate interactions between the major controls on large scale processes functioning over long periods of time in complex drainage basins

predicting fine sediment dynamics along a pool riffle mountain channel abstract fine sediment dynamics in mountain rivers are of concern because of implications for aquatic habitat channel stability and downstream sediment yields many mountain river systems have episodic fine sediment transport because of infrequent point source sediment inputs from landslides basin instability triggered by land uses such as logging or infrequent mobilization of the coarse surface layer in channels dam removal which is now more likely along mountain rivers may also provide a substantial fine sediment input to downstream channel reaches fine sediment storage in the interstices of spawning gravels and within pools along mountain rivers is of particular interest because of impacts to aquatic organisms in this study we focus on sediment dynamics within pools of the north fork poudre river in colorado as an example of the processes controlling fine sediment deposition storage and transport within laterally constricted pools the 1996 release of 7000 m3 of silt to gravel sized sediment from a reservoir on the north fork provided an opportunity to develop a field data set of fine sediment dynamics and to test the predictions of three different one or two dimensional sediment transport and hydraulic models against the field observations the models were calibrated against quantitative measurements of pool scour and fill one dimensional hec 6 results indicate that robust simulations yield the greatest agreement between predicted and measured pool bed elevation change model calibration on two pools and validation on one pool indicate that at least 58 of observed bed changes after the sediment release were predicted by hec 6 modeling accuracy using quasi two dimensional gstars 2 0 was considerably more variable and no pool wide trends were obtained the two dimensional model rma2 substantially improved the representation of eddy pool hydraulics within a compound pool of the north fork results from the hydraulic modeling coupled with bed load and total load computations delineate areas of scour and deposition which are consistent with observations in the field a conceptual model of sediment delivery and storage for laterally confined pools suggests that persistent deposition of fine sediment within eddies distal from the sediment source may result from sediment releases the original loss of channel capacity facilitated additional deposition within eddies as sediment within upstream proximal pools became mobilized at high discharges the development of a strong shear zone prevents degradation of sediment deposits within the eddy central portions of these proximal pools may clear according to existing models whereas deposition within recirculating zones may be long term water managers could use these models to estimate minimum pool volume for overwinter habitat and residence time of pool sediment