reach scale sediment transfers an evaluation of two morphological budgeting approaches this paper compares two approaches used to derive measures of annual sediment transfers within a 1 km long piedmont reach of the gravel bed river coquet in northumberland northern england the techniques utilize i channel planform and cross section surveys based on a theodolite electronic distance measurement edm survey of 21 monumented channel cross sections and channel and gravel bar margins and ii theodolite edm survey generating a series of x y z coordinates from which digital elevation models dems of the reach were constructed calculating the difference between dem surfaces provided a measure of volumetric change between surveys carried out during the spring of 1999 and 2000 the use of kriging in dem generation and differencing permits computation of estimate variances and confidence intervals for sediment transfer error analysis validating the dems using surveyed cross sections indicated a mean error between surveyed and dem generated cross sections of around twice the value of the d50 of the surface sediment in the reach comparison of sediment volumes derived from the two approaches suggests that compared with the dem method monumented cross sections underestimate the magnitude of volumetric changes that occur within the reach the cross section approach relies on a simplistic integration of the volumes whereas dem differencing provides an estimate at a resolution under the control of the analyst furthermore the cross section approach does not permit a reliable estimate of the uncertainty of the volumes calculated in addition the dem methodology based on the morphological unit scale provides an explicit identification of spatial patterns of erosion and deposition a feature that cross section based approaches may fail to include copyright 2003 john wiley sons ltd

mineralogy and mineral chemistry of bi minerals constraints on ore genesis of the beiya giant porphyry skarn gold deposit southwestern china abstract the beiya deposit located in the sanjiang tethyan tectonic domain sw china is the third largest au deposit in china 323 t au 2 47 g t as a porphyry skarn deposit beiya is related to cenozoic himalayan alkaline porphyries abundant bi minerals have been recognized from both the porphyry and skarn ores comprising bismuthinite bi cu sulfosalts emplectite wittichenite bi pb sulfosalts galenobismutite cosalite bi ag sulfosalt matildite bi cu pb sulfosalts bismuthinite derivatives bi pb ag sulfosalts lillianite homologs galena matildite series and bi chalcogenides tsumoite the unnamed bi 2 te the unnamed ag 4 bi 3 te 3 tetradymite and the unnamed bi pb 3 te s 4 native bismuth and maldonite are also found in the skarn ores the arsenopyrite geothermometer reveals that the porphyry au mineralization took place at temperatures in the range of 350 450 c and at log f s 2 in the range of 8 0 to 5 5 respectively in contrast the beiya bi mineral assemblages indicate that the skarn ore forming fluids had minimum temperatures of 230 175 c prevailing temperatures exceeding 271 c and fluctuating f s 2 f te 2 conditions we also model a prolonged skarn au mineralization history at beiya including at least two episodes of bi melts scavenging au we thus suggest that this process was among the most effective au enrichment mechanisms at beiya

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

fluid inclusion and stable isotope c o and s constraints on the genesis of the high grade langdu cu skarn deposit in yunnan sw china abstract the langdu cu skarn deposit is the highest grade cu deposit average 6 49 cu in the zhongdian polymetallic district in sw china skarns and ore bodies occur primarily in the contact zone of upper triassic qugasi formation fm and late triassic ca 217 ma intrusions disseminated massive stockwork and vein like sulfide ores occur in the skarn quartz calcite veins porphyry and marble skarn minerals include pyroxene garnet actinolite and epidote four types six subtypes of fluid inclusions fis are identified in the sulfide bearing quartz veins type i liquid rich two phase fis have varying vapor liquid ratios and yielded homogenization temperatures of 110 338 c and salinities of 1 7 29 5 wt nacl eqv type ii vapor rich fis contain ch4 n2 bubbles and homogenized to vapor at 262 425 c type iii fis are single phase at room temperature 20 c a vapor phase is present at below 120 c and the fis homogenized at 117 to 114 c type iv daughter mineral bearing fis homogenized by halite disappearance at 295 392 c and have salinities of 37 8 46 6 wt nacl eqv such characteristics suggest that fis were trapped by fluid immiscibility and phase separation the 34scdt values of chalcopyrite and pyrrhotite are of 5 3 to 0 7 on the 34s histogram all langdu data show a cluster of 32s rich 34scdt 5 3 to 4 6 and a cluster of 34s rich 34scdt 1 1 to 0 7 type i calcite in skarn and type ii calcite in quartz sulfide vein have 13cpdb and 18osmow values of 8 4 to 7 8 6 3 to 6 1 and 10 1 to 12 3 and 12 0 to 13 0 respectively type iii calcite from calcite sulfide veins has 13cpdb 5 6 to 0 2 and 18osmow 12 5 to 16 3 biotite garnet and pyroxene syn ore quartz and chlorite yielded 18osmow values of 6 9 4 1 5 13 2 15 3 and 6 8 respectively sulfur carbon and oxygen isotopic features of these hydrothermal minerals and the fis microthermometric data suggest that the ore forming fluids were magmatic sourced and contaminated by meteoric formation water during ascent and or fluid wallrock interactions low 34s 5 3 to 4 6 in sulfides and the ch4 in the fis are interpreted to reflect the reaction between the magmatic fluids and the carbonaceous slate in qugasi fm the methane likely expanded the vapor liquid immiscibility field and reduced the sulfates so42 to sulfides s2 and extensive water rock reaction and fluid mixing may have occurred leading to the high grade cu mineralization at langdu

high salinity fluid inclusions in the yinshan polymetallic deposit from the le de metallogenic belt in jiangxi province china their origin and implications for ore genesis a fluid inclusion investigation of the polymetallic mineralization at yinshan from the le de metallogenic belt in jiangxi province of china has been carried out using petrographic and microthermometric techniques the data obtained here indicate that three major types of fluids were involved during the formation of the deposit they are type i vapor rich type ii liquid rich and type iii halite bearing inclusions within the h2o nacl system the high salinity fluids represented by type iii inclusions being unusual to the distal part of an intrusion centered ore forming system such as yinshan have been interpreted as the product of direct exsolution of a crystallizing magma rather than a result of fluid immiscibility from a low salinity fluid evidence used to support such an interpretation includes the mode of homogenization of type iii inclusions exclusively via halite dissolution spatial separation of type i and type iii inclusions on microscopic scale the consistent phase ratios within the inclusions concerned and considerable deviation in homogenization temperature for both type i and type iii inclusions trapping conditions for type i inclusions were estimated to be around 440 degrees c and 260 bars while type iii inclusions were constrained to be trapped at least above 900 bars and 500 degrees c the formation temperatures for type ii inclusions range from 270 to 390 degrees c if a lithostatic pressure of 260 bars is assumed pressure fluctuation determined by this fluid inclusion study coupled with decreases in salinity and temperature as result of the potential fluid mixing are supposed to have played an important role in triggering the precipitation of ore minerals from the hydrothermal solution c 2006 elsevier b v all rights reserved

a kuroko type polymetallic sulfide deposit in a submarine silicic caldera manned submersible studies have delineated a large and actively growing kuroko type volcanogenic massive sulfide deposit 400 kilometers south of tokyo in myojin knoll submarine caldera the sulfide body is located on the caldera floor at a depth of 1210 to 1360 meters has an area of 400 by 400 by 30 meters and is notably rich in gold and silver the discovery of a large kuroko type polymetallic sulfide deposit in this arc front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits

ore genesis of the late cretaceous larong porphyry w mo deposit eastern tibet evidence from in situ trace elemental and s pb isotopic compositions abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 a newly discovered deposit in the easternmost bangong nujiang metallogenic belt bnmb is located in eastern tibet the w mo mineralization occurs as veins and stock works hosted in monzogranite porphyry granodiorite porphyry and surrounding quartz schist and can be divided into two main paragenetic stages the w mineralization stage stage i consists of various k feldspar quartz scheelite veins and the quartz sulfide stage stage ii is dominated by molybdenite and pyrite of which the latter can be further subdivided into three sub stages here we present la icpms in situ trace elements and s pb isotopes of sulfides from the larong deposit in order to constrain the sources of ore forming elements and the processes of mineralization our study shows that pyrite is rich in co and as molybdenite is rich in w pb and bi and chalcopyrite has high sn contents these results are consistent with the mineralization characteristics of the larong deposit where the main metallogenic elements are w and mo accompanied by bi sn and cu overall sulfides from the larong deposit have calculated 34svcdt values ranging from 0 25 to 6 37 suggesting a predominantly magmatic origin for sulfur from stage ii 1 to stage ii 2 to stage ii 3 the average 34svcdt values of pyrite change from 0 33 to 1 88 to 5 34 showing a progressive and gradual change in redox and temperature conditions molybdenite has high pb isotopic ratios 208pb 204pb 39 356 39 908 207pb 204pb 15 747 15 928 206pb 204pb 18 843 20 120 but low re contents and pyrite has low ni contents implying that the ore forming materials were mainly derived from the crust we propose that the w mo mineralization is genetically related to the late cretaceous monzogranite porphyry with the mineralization of w and mo occurring as a result of decreases in temperature and oxygen fugacity of the ore forming fluid exsolved from the magma in combination with previous studies our study led to the identification of three w dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the bnmb

distance of movement of coarse particles in gravel bed streams distributions of distance of bedload particle movement were examined in two gravel bed streams using several hundred magnetically tagged cobbles and pebbles the compound poisson model of einstein hubbell sayre and a simple gamma function model were compared with observed distributions of moved particles and of all particles both models fit the data reasonably well for small mean displacements but notable misfits occurred in an event with large mean displacement when mean particle travel distance approaches the scale of bar spacing trapping in the bars interrupts particle progress and the dispersion process the data remain very noisy so definitive discrimination of suitable models will require trials with more than 103 particles

magmatic evolution and related w mo mineralization in the larong deposit eastern tibet evidence from zircon u pb ages geochemistry and sr nd hf isotopes abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 is the first discovered giant w mo deposit in the leiwuqi zogang metallogenic belt sanjiang region multi stage granitoids including the dacite porphyry dp granodiorite porphyry gp biotite granite porphyry bgp monzogranite porphyry mp biotite granite bg and granite aplite ga have been identified in the larong deposit however the magmatic evolution and related w mo mineralization in this deposit are still poorly understood la icp ms zircon u pb dating of the dp gp bgp mp bg and ga yield weighted mean 206pb 238u ages of 214 0 0 7 ma 213 8 1 3 ma 104 4 0 9 ma 93 9 1 3 ma 91 7 0 5 ma and 36 2 0 6 ma respectively the late triassic dp and gp should be classified as peraluminous a cnk values of 0 95 1 57 s type granitoids they are characterized by pronounced negative end t values 10 01 to 13 92 and ehf t values 8 5 to 16 6 with old tdm2 nd and tdm2 hf ages 1 81 2 12 ga and 1 79 2 30 ga respectively indicating that the dp and gp were mainly derived from partial melting of ancient crustal materials after break off of the paleo tethyan oceanic slab the late cretaceous bgp mp and bg and late eocene ga have low a cnk ratios 0 92 1 06 but high sio2 70 57 77 34 and differentiation index di 87 55 98 06 similar to the characteristics of highly fractionated i type granite detailed elemental e g depletion in nb ta ti sr ba eu and p and isotopic data 87sr 86sr i 0 71192 0 72932 end t 11 81 to 9 11 ehf t 10 4 to 1 4 demonstrate that they were the result of magma mixing between ancient crust derived melts and mantle derived melts the bgp was produced during the final stage of bangong nujiang tethyan ocean bnto subduction the mp and bg were formed under a post collisional tectonic setting related to slab break off of the bnto and the ga was likely associated with delamination of the thickened eclogitic lower crust together with lithospheric mantle the w mo mineralization in the larong deposit is genetically associated with the mp with four favorable factors that can account for the formation of this deposit 1 high w background 2 multi stage magmatism 3 highly evolved relatively oxidized and f rich magmatic system and 4 sufficient calcium obtained by intense fluid rock interaction

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

sanjiang tethyan metallogenesis in s w china tectonic setting metallogenic epochs and deposit types abstract tectonically the sanjiang tethyan metallogenic domain stmd is located within the eastern himalayan tibetan orogen in the sanjiang tethys southwestern china although this metallogenic domain was initiated in the early palaeozoic extensive metallogenesis occurred in the late palaeozoic late triassic and himalayan tertiary epochs corresponding tectonic settings and environments in the domain are an arc basin system related to the subduction of the palaeo tethyan oceanic slabs a post collision crustal extension setting caused by the lithospheric delamination or slab breakoff underneath the sanjiang tethys during the late triassic large scale strike slip faulting and thrusting systems due to the indo asian continent collision since the palaeocene in this metallogenic domain important gold copper base metals rare metals and tin ore belts incorporating a large number of giant deposits were developed the main types of deposits include 1 porphyry copper deposits controlled by a large scale strike slip fault system 2 vhms deposits mainly occurring in intra arc rift basins and post collision crustal extensional basins 3 shear zone type gold deposits in the ophiolitic melange zone along the thrusting shearing system 4 hydrothermal silver polymetallic deposits in the triassic intra continental rift basins and tertiary strike slip pull apart basins and 5 himalayan granite related greisen type tin and rare metallic deposits within the metallogenic epochs of the late palaeozoic to cenozoic the styles and types of the ore deposits changed from vhms types in the late palaeozoic through exhalative sedimentary type deposits in the late triassic to porphyry type copper deposits shear zone type gold deposits hydrothermal vein type silver polymetallic deposits greisen type tin and rare metal deposits in the cenozoic correspondingly ore forming metals also changed from a pb zn cu ag association through ag cu pb zn fe ag pb and ag au hg associations to ag cu pb zn cu mo au sn and li rb cs nb zr hf y ce sc associations

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

himalayan cu mo au mineralization in the eastern indo asian collision zone constraints from re os dating of molybdenite we present new re os molybdenite age data on three porphyry cu mo au deposits yulong machangqing and xifanping these deposits are associated with the himalayan adakitic magmatism that occurred in a continental collision environment controlled by large scale cenozoic strike slip faults in the eastern indo asian collision zone three distinct episodes of cu mo au mineralization are recognized at yulong re os isotopic data of four molybdenite samples from sulfide quartz veins in the quartz sericite alteration zone yield an isochron with an age of 40 1 1 8 ma 2 coincident to a zircon sensitive high mass resolution ion microprobe shrimp age of 40 9 0 1 ma for the host monzogranite the molybdenite re os dates together with k ar rb sr u pb and 40ar 39ar dates on the pre and intra ore porphyries suggest that cu mo au mineralization formed during the late stage 40 ma of regional porphyry magmatism but hydrothermal activity probably lasted to at least 36 ma at machangqing molybdenite re os data from the k silicate and quartz sericite alteration zones yield an isochron with an age of 35 8 1 6 ma 2 which is identical to the zircon shrimp and bulk rock rb sr ages 35 36 ma of the host granite but older than bulk rock k ar dates 31 32 ma for associated au bearing quartz syenite with advanced argillic alteration at xifanping five molybdenite samples from the k silicate alteration zone yield the youngest re os isochron age in the area at 32 1 1 6 ma 2 the re os molybdenite dates here are younger than k ar ages 33 5 34 6 for hydrothermal biotite and actinolite there is a positive correlation between the absolute age of the deposits and their cu and au reserves in the eastern indo asian collisional zone episodic stress relaxation probably caused multiple magmatic intrusions which most likely resulted in three episodes of cu mo au mineralization in the eastern indo asian collision zone

gravel transport and morphological change in braided sunwapta river alberta canada the relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial sunwapta river alberta canada there are two major periods of morphological change each lasting several days and each involving the complete destruction and reconstruction of bar complexes bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream reconstruction involved accretion of unit bars on bar head flank and tail and in one case was initiated by disection of a large lobate unit bar high rates of sediment movement measured from net scour and fill of the cross sections coincided with these morphological changes sediment was supplied from both bed and bank erosion and patterns and distances of transfer were highly variable rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step length approach or a sediment budget measurements of scour and fill and observations of morphological change indicate that step lengths virtual transport distances were typically 40 100m during a diurnal discharge cycle shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach averaged transport rates mean bedload transport rates correlate with discharge but with considerable scatter the largest deviations from the mean relation can be tied to phases of channel incision bank erosion scour hole migration bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream independent of discharge these are interpreted as field evidence of autopulses or macropulses in bedload transport previously observed only in laboratory models of braided streams

bedload entrainment travel lengths step lengths rest periods studied with passive iron magnetic and active radio tracer techniques this paper reports results from bedload transport investigations with active radio and passive iron magnetic tracers in the lainbach a step pool mountain river in bavaria southern germany the spatial distributions of the iron tracers after flood events can be best described by exponential or gamma distributions there is some indication of a tendency of size selective transport of the iron tracers but there is also a considerable amount of scatter in the correlations between weight size and travel length owing to the masking influence of other variables such as the shape of the particles and different positions in the river bed the experiments with artificial magnetic tracers showed that elongated pebbles rods had the longest mean transport distance platy ones discs remained relatively close to the starting points the particles from the pool showed the greatest transport lengths and a 100 per cent chance of being eroded the pebble transmitter system petsy consists of transmitters implanted into individual pebbles a computerized receiver a stationary antenna system with an antenna switchboard and a data logging system the particles do not move continuously but in a series of transport steps and non movement intervals a single value for a given size class is not adequate to describe the critical conditions of entrainment under natural circumstances a probability approach is much more suitable the critical unit discharges total discharge divided by active channel width along the measuring reach are dependent on river bed morphology in the steps bedload needs higher unit discharges to be entrained once entrained the transport of bedload is stochastic in nature and the single particle transport is controlled by the step lengths and the duration of rest periods the distributions of both parameters can be approximated by exponential functions applying the stochastic concept proposed by einstein the mean values of the random variables step length and duration of rest period measured with the petsy technique were used for the simulation of spatial distributions of bedload particles from point sources more field and laboratory data are needed to include varying flow and roughness conditions with tracers representing different particle characteristics

the okinawa trough genesis of a back arc basin developing along a continental margin abstract the okinawa trough is the only example of a marginal back arc basin type at a young stage of evolution that developed along a continental margin the first phase of crustal stretching and subsidence occurred during late miocene early pliocene times a second major phase occurred after the latest pliocene or early pleistocene with en echelon rift axes along the axes of the okinawa trough oblique to the general trend of the arc and trench crustal separation and active spreading has occurred in the central and southern okinawa trough but the north okinawa trough is only in a rifting stage the development of the basin has several correlations with the general tectonism of the arc system 1 1 there was a synchronism between opening and subsidence of the okinawa trough and tilting and subsidence of the fore arc terrace 2 2 back arc rifting was initiated in the volcanic arc and propagated along it during the neogene remnants of a volcanic arc are found on the continental side of the basin the beginning of the back arc spreading observed in the central and southern okinawa trough correspond to a relative minimum in the activity of the volcanic arc 3 3 the timing and kinematic evolution of the taiwan collision and the south okinawa trough opening suggest a connection between these two events such a collision lateral back arc opening model could explain the initiation of the opening of back arc basins but additional phenomena such as thermal convection retreating trench model or anchored slab model are indispensable to maintain extension in the back arc basin

variability of the path of the kuroshio ocean current over the past 25 000 years the kuroshio current is the strong northwestern component of the subtropical north pacific ocean gyre and advects a large amount of heat from the tropics to northern mid latitudes the kuroshio has bimodal stationary flow patterns with small and large meander paths east of central japan1 2 which switch on annual and decadal timescales3 4 these switches seem to be caused by changes in current velocity and volume transport of the north equatorial current that are associated with variations in the trade wind intensity in the eastern equatorial north pacific ocean5 6 here we present alkenone derived sea surface temperature records at multicentennial resolution from sediment cores from the nishishichitou ridge off central japan these 25 000 year records show that the kuroshio path has also fluctuated on millennial timescales this variability resembles that of the subtropical high pressure of the north pacific reconstructed from terrestrial pollen distributions water levels in north american lakes and marine micropalaeontological records7 together these data indicate that climate variability off central japan over the past 25 000 years may be part of a circum pacific phenomenon reflecting the rate of subtropical surface circulation in the north pacific ocean

size and distance of travel of unconstrained clasts on a streambed we have examined the relation between the mean distance of movement during individual flood events and the mean particle size of unconstrained clasts in gravel bed rivers distance of movement was scaled using the mean distance of movement of the median size group of the surface material size was scaled using the median b axis diameter of the subsurface material the scaled data are fitted with a nonlinear function clasts larger than the median of surface material exhibit a steep decline of mobility with an upper limit for mobility near di d50sub 10 smaller materials exhibit a less sensitive relation we suppose that trapping of small clasts affects their travel distance these results indicate that the movement of free surface stones is size preferred a subordinate analysis of free constrained and buried particles reveals that bed surface structure acts to reduce differential movement

unequal mobility of gravel and sand in weakly bimodal river sediments bed load was trapped during flood events over a 20 month period at the lower end of the allt dubhaig a small river in scotland with rapid downstream fining of gravel bed material on a slowly aggrading concave long profile the channel bed near the trap is predominantly gravel with a secondary sand mode total transport in each event depended mainly on peak shear stress rather than duration over a threshold bed load was mainly sand in smaller events bimodal in intermediate events and mainly gravel in the biggest floods mean and maximum grain diameter both increased with peak shear stress but in different ways analysis of fractional transport rates and maximum grain size in relation to peak shear stress suggests that gravel transport is slightly size selective but sand transport is close to equal mobility the slight selectivity in gravel transport is consistent with previous field studies of near equilibrium unimodal beds and supports assumptions made in the numerical model of hoey and ferguson 1994 which successfully simulates the observed amount of downstream fining over the 2 5 km upstream of the bed load trap

quantitative determination of the activity of within reach sediment storage in a small gravel bed river using transit time and response time abstract reach scale sediment storage is rarely quantified in sediment budget studies yet it has a considerable effect on the sediment delivery ratio at the basin scale and on the accuracy of morphological methods of bedload estimation at the reach scale deployment of magnetic tracer particles allows accurate characterisation of sediment fluxes in gravel bed rivers and provides the opportunity to quantify storage activity using reservoir theory activity was quantified at reach and sub reach scales in two reaches of a small gravel bed river and the possibility of quantifying the activity of smaller scale sediment stores is explored reach scale transit time functions were derived from the cumulative output of sediment against age or time the shape of the functions in both reaches was determined by flood incidence and magnitude hydraulics sediment tracer availability grain size and local morphology accurate transit time functions were difficult to determine due to reliance upon tracer output and the associated problems of tracer exhaustion over time and imperfect tracer recovery rates in addition if tracers of different ages are allowed to mix for example where upstream input is possible then the resultant transit time distributions age are not comparable with the timing of the hydraulic processes responsible unless the hydraulic conditions are constant these results suggest that transit time is difficult to determine from tracer studies in gravel bed rivers consequently a refinement of transit time the response time is introduced and is defined as the time after the initial input of tracer sediment when cumulative tracer output exceeds the amount of tracer sediment remaining in storage whilst still based upon tracer output the calculation of response time also utilises storage data and is expressed relative to time since the start of the study rather than age it is therefore directly comparable with the incidence of hydraulic conditions this provides a more informative measure of activity which is readily available from tracer data in gravel bed rivers and allows evaluation of the importance of flood incidence and magnitude grain size morphology and reach characteristics stability like transit time response time estimates are hindered by mixing of sediment of different ages at the sub reach scale however it does account for errors from less than 100 recovery and tracer exhaustion more effectively than transit time quantification of absolute and relative size effects in transport is also possible from response time

zircon u pb ages hf o isotopes and whole rock sr nd pb isotopic geochemistry of granitoids in the jinshajiang suture zone sw china constraints on petrogenesis and tectonic evolution of the paleo tethys ocean the jinshajiang suture zone located in the eastern part of the tethyan tectonic domain is noticeable for a large scale distribution of late jurassic to triassic granitoids these granitoids were genetically related to the evolution of the paleo tethys ocean beiwu linong and lunong granitoids occur in the middle zone of the jinshajiang suture zone and possess similar geochemical features indicating that they share a common magma source sims zircon u pb dating reveals that the beiwu linong and lunong granitic intrusions were emplaced at 233 9 1 4 ma 2 233 1 1 4 ma 2 and 231 0 1 6 ma 2 respectively all of these granitoids are enriched in abundances of si sio2t 65 2 73 5 wt and large ion lithophile elements liles but depleted in high field strength elements contents hfses e g nb ta and ti in addition they have low p2o5 contents 0 06 0 11 wt a cnk values molecular al2o3 cao na2o k2o mostly 1 1 and 10 000 ga al ratios 1 7 2 2 consistent with the characteristics of i type granites in terms of isotopic compositions these granitoids have high initial 87sr 86sr ratios 0 7078 0 7148 pb isotopic compositions 206pb 204pb t 18 213 18 598 207pb 204pb t 15 637 15 730 and 208pb 204pb t 38 323 38 791 zircon 18o values 7 3 9 3 and negative end t values 5 1 to 6 7 suggesting they were predominantly derived from the continental crust their nb ta ratios average value 8 6 are consistent with those of the lower continental crust lcc however variable ehf t values 8 6 to 2 8 and the occurrences of mafic microgranular enclaves mmes suggest that mantle derived melts and lower crustal magmas were involved in the generation of these granitoids moreover the high pb isotopic ratios and elevated zircon 18o values of these rocks indicate a significant contribution of the upper crustal composition we propose a model in which the beiwu linong and lunong granitoids were generated under a late collisional or post collisional setting it is possible that this collision was completed before late triassic decompression induced mantle derived magmas to be underplated and provided the heat for the anatexis of the crust hybrid melts including mantle derived and the lower crustal magmas were then generated the hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rock assimilation such three component mixing magma source and subsequent fractional crystallization could be responsible for the formation of the beiwu linong and lunong granitoids

tracing river gravels insights into dispersion from a long term field experiment abstract sediment dispersion is a fundamental component of the sediment transfer process in gravel bed rivers modeling this process requires an understanding of the collective movement of mixed size clasts this study explores the temporal evolution of gravel dispersion to underscore the importance of field observation in informing modeling efforts magnetically tagged gravels deployed in carnation creek have been monitored repeatedly over 17 years four metrics used to describe the extent of dispersion document that the overall shape in the spatial distribution of grain location changes over time the general trends mask the complexity of the dispersion process expressed by channel sections where tracers are concentrated regardless of grain size the distribution of total grain displacement responsible for dispersion evolves as tracers become well mixed results demonstrate that observations from the field are crucial to the understanding and modeling of sediment dispersion because they provide key insights into the dispersion process that must be known a priori for mathematical modeling and similar observations cannot be collected using laboratory flumes

the timing and magnitude of coarse sediment transport events within an upland temperate gravel bed river this paper describes the application of a new instrument to continuously measure bedload transport an impact sensor to a 72 km2 test catchment in the yorkshire dales northern england data from a network of impact sensors are linked to repeat surveys of channel morphological response to get a better understanding of the conditions that lead to sediment generation and transfer results suggest certain areas of the catchment act as key sediment sources at the annual time scale with material being quickly delivered to the lower parts of the catchment along the steep bedrock channel sediment transfer within the tributaries occurs in significantly smaller magnitudes than within the main channel but it moves more frequently and at different times of the year with transfer rates being strongly conditioned by larger scale valley geomorphology the lower 5 6 km reach sees a significant reduction in gradient and a widening of the valley this permits significant accumulation within the channel which has persisted for many years this lower reach is very sensitive to changes in sediment supply and there is good agreement between changes in bedload transport data and the surveyed channel response these observations have major implications for how river management projects should be developed in upland environments especially those where large scale geomorphological controls have a major impact upon the sediment transfer process evidence suggests that where river management restricts lateral movement of the channel and transfer of sediment into floodplain storage changes in sediment supply can lead to areas of severe accumulation acceleration of bank erosion and exacerbated flood risk

sediment routing analyses based on chronological changes in hillslope and riverbed morphologies recent studies of sediment delivery and budgets in the united states indicate that upland erosion rates at a given time may not explain contemporaneous sediment yields from a drainage basin this suggests temporal discontinuities in sediment delivery associated with hillslope and channel storage processes integration of sediment production storage and transport is essential to understand sediment routing in basins we analysed each process chronologically using aerial photographs monitoring data of sediment movement and annual tree rings and then compared estimated temporal changes in sediment production from hillslopes floodplain disturbance areas and sediment transport in river channels toeslopes floodplains and alluvial fans together contained 59 per cent of sediment eroded from uplands over the last 30 years monitoring results of riverbed changes showed that the volume of stored sediment on floodplains decreased exponentially with succeeding floods the age distribution of floodplain deposits reflected the disturbance history of a river channel and followed an exponential decrease with age the results of this study may have important implications for sediment control plans for watersheds in steep regions

redox controlled generation of the giant porphyry cu au deposit at pulang southwest china some porphyry cu au deposits with relatively reduced ore assemblages characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite are generally considered to be associated with reduced i type granitoids however the role of magmatic oxygen fugacity fo2 in controlling cu au mineralization in such reduced porphyry deposits is poorly understood the giant late triassic ca 216 ma pulang porphyry cu au deposit of southwest china shows typical reduced ore assemblages this study reported the systematical variation of upper crustal magmatic fo2 of pulang deposit based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization related porphyries early p1 and late p2 porphyry results indicate that magma of the mineralization related porphyries experienced complex fo2 fluctuations during its upper crustal evolution the early primary magma had very high initial fo2 with fmq 3 0 at depths of 12 km fmq is the deviation of logfo2 from the fayalite magnetite quartz fmq buffer the fo2 of evolved parental magma subsequently decreased with fmq 1 9 due to injection of relatively reduced dioritic magmas fmq 1 4 to 2 3 from a deeper chamber 17 21 km depth into the primary magma chamber at 10 12 km depth magma mixing had largely ceased at 6 10 km depth the parental magma then ponded within the reduced tumugou formation at a depth of 3 7 km where magmatic fo2 decreased to a moderately oxidized state fmq 1 6 and finally to a moderately reduced state reflected by log fe2o3 feo ratios of 0 5 for p2 porphyry results of this study of magmatic fo2 indicate that porphyry magmas associated with reduced pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the tumugou formation the sharp fo2 decrease at very shallow depth prevented the early loss of cu and au because the magma remained oxidized until it was emplaced at 3 7 km depth moderately reduced magmas may thus have a genetic association with porphyry cu au mineralization

mineralogy of bi sulfosalts and tellurides from the yaoan gold deposit southwest china metallogenic implications abstract bismuth sulfosalts and tellurides are commonly present in many hydrothermal gold deposits and can provide important genetic and physicochemical constraints on the metallogenesis the abundant auriferous specular hematite veins in the yaoan gold deposit of the jinshajiang red river alkaline porphyry metallogenic belt southwest china contain an assemblage of bi sulfosalts and tellurides together with hematite pyrite and chalcopyrite bismuth sulfosalts are characterized by replacement textures resulting from changes of fluid composition e g pb bi cu and ag and mainly include bismuthinite derivatives e g bismuthinite paarite krupkaite lindstromite and friedrichite aikinite pad raite cuprobismutite homologues probably submicroscopic intergrowths of hodrushite and cuprobismutite and emplectite tellurides are tiny comprising tsumoite melonite hessite and calaverite which coexist with bismuthinite derivatives these bi sulfosalts and tellurides have direct contact with gold indicating that the yaoan gold metallogenesis was likely linked to the syenite porphyry magmatism that was originally sourced from a regional lithospheric mantle probably metasomatized by subduction of te rich sediments the telluride assemblage also reveals that the gold was precipitated under oxidizing conditions that has a high tellurium fugacity at the beginning fte2 10 7 9 and fs2 10 8 5 at 300 c

european phanerozoic metallogenesis phanerozoic metallogenesis in europe displays divergent characteristics which may be related to the variable nature of the three great european phanerozoic orogens caledonian variscan and alpine these reflect different geodynamic processes the caledonian orogen resulted from the interaction of essentially oceanic with continental lithosphere whilst the variscan and alpine orogens evolved mainly from continent continent collisions with the involvement of a series of smaller oceanic basins each major stage of the orogenic processes is characterised by a typical metallogeny the occurrence of subduction related processes in the caledonian orogeny gave rise to extensive vhms deposition with characteristic zn cu ratio signatures the relative lack of abundance of metal rich andean type porphyry type mineralisation remains unexplained unless present erosional levels have prevented the preservation of such deposits continent continent collisions do not appear to result in extensive mineralisation unless elevated heat flows result possibly as a result of lithospheric delamination at the peak collisional stage the development of late stage and peri orogenic sedimentary basins are characterised by extensive pb zn ba f mineralisation as expressions of basinal fluid flow of regional dimensions

size selective entrainment of bed load in gravel bed streams entrainment of mixed size gravel bed material was studied in nine reaches of three high power streams in scotland and norway paired measurements of at a point shear stress estimated from velocity profiles and bed load transport by hand held sampler were made they extended to very high values 400 n m 2 3 5 kg m x s x analyses of maximum bed load diameter mean bed load diameter transport rates of individual size fractions and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size despite strong relative size effects precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates size selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to be significant

relationships between porphyry cu mo mineralization in the jinshajiang red river metallogenic belt and tectonic activity constraints from zircon u pb and molybdenite re os geochronology abstract the jinshajiang red river porphyry cu mo metallogenic belt is an important cenozoic porphyry cu mo mineralization concentrating zone in the eastern indo asian collision zone new zircon u pb and molybdenite re os ages and compilation of previously published ages indicate that porphyry cu mo deposits in the belt did not form at the same time i e the porphyry emplacement and relevant cu mo mineralization ages of the ailaoshan red river ore belt in south range from 36 3 ma to 34 6 ma and from 36 0 ma to 33 9 ma respectively which are obviously younger than the porphyry emplacement ages of 43 8 36 9 ma and the relevant cu mo mineralization ages of 41 6 35 8 ma of the yulong ore belt in north tectonic studies indicated that the jinshajiang fault system in north and ailaoshan red river fault system in south of the jinsjiang red river belt had different strike slip patterns and ages the right lateral strike slip motion of the jinshajiang fault system initiated at ca 43 ma with corresponding formation of the yulong porphyry cu mo system whereas the left lateral strike slip motion of the ailaoshan red river fault system initiated at ca 36 ma with corresponding formation of the ailaoshan red river porphyry cu mo system therefore the different ages of porphyry cu mo systems between in north and south of the jinshajiang red river belt indicate that the porphyry cu mo mineralization is closely related to the divergent strike slip movements between the jinshajiang and ailaoshan red river strike slip faulting resulted from the indo asian collision the tanslithospheric jinshajiang red river faulting caused partial melting of the enriched mantle sources of alkali rich porphyries by depressurization or and asthenospheric heating and facilitated the migration of alkali rich magmas and the corresponding formation of alkali rich porphyries and relevant cu mo deposits in the belt

channel morphology and bedload pulses in braided rivers a laboratory study bedload pulses in gravel bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology bedload transport and channel morphology were measured in a small scale generic model of braided gravel bed streams two experiments are described in which braided channels developed in a 14 m 3 m sand tray total bedload output from the tray was weighed every 15 minutes stream bed geometry was surveyed every four hours pulses were observed in the bedload output time series and were qualitatively related to the channel morphology immediately upstream of the measuring section the bagnold 1980 bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading underprediction occurred when applied to degrading channels aggradation was associated with channel multiplication and bar deposition channel pattern simplification occurred when degradation took place and bars emerged from the water flow development of phases of aggradation and degradation is dependent upon the three dimensional geometry of the stream beds spatial and temporal feedback loops can be identified enabling links between channel morphology and bedload transport rate to be directly identified

a field experiment on the development of sedimentary structures in a gravel bed river in gravel bed rivers bed sedimentary structures exert a significant influence on the stability of the bed particle motion and stream dynamics a detailed description of the development of sedimentary structures is essential to define the overall activity of sediment transport this paper aims to improve our understanding of the dynamics of sedimentary structures at the reach scale using a field approach the objectives of the study are 1 to describe the processes of sedimentary structures development from a manipulated bed surface and 2 to show the effect of keystones on the development of the sedimentary structures by monitoring the displacement of individual tagged particles we investigated the dynamics of sedimentary structures in three 15 m long reaches of a small gravel bed river characterized by moderate slope and high relative roughness the bed material is composed of a range of gravel sizes with sparse boulders that remain immobile during most flows we have disrupted the bed surface material of the first reach to create a disorganized bed surface two reaches where the bed material remained undisturbed were used as control sections detailed topographic maps and passive transponders were used to describe the formation processes of sedimentary structures the initial manipulations of the bed led to a more fragmented surface in the experimental section however sedimentary structures developed very quickly with an equilibrium bed surface developing after only two sediment transport events of low magnitude discharge this rapid adjustment of the bed is associated with the development of key sedimentary structures anchored by the large boulders at the reach scale these structures increased the probability of congested areas in the displacement of bed material in both control sections sedimentary structures were maintained during the experiment copyright 2007 john wiley sons ltd

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

post collisional crustal extension setting and vhms mineralization in the jinshajiang orogenic belt southwestern china abstract the jinshajiang orogenic belt job of southwestern china located along the eastern margin of the himalayan tibetan orogen includes a collage of continental blocks joined by paleozoic ophiolitic sutures and permian volcanic arcs three major tectonic stages are recognized based on the volcanic sedimentary sequence and geochemistry of volcanic rocks in the belt westward subduction of the paleozoic jinshajiang oceanic plate at the end of permian resulted in the formation of the chubarong dongzhulin intra oceanic arc and jamda weixi volcanic arc on the eastern margin of the changdu continental block collision between the volcanic arcs and the yangtze continent block during early middle triassic caused the closing of the jinshajiang oceanic basin and the eruption of high si and al potassic rhyolitic rocks along the permian volcanic arc slab breakoff or mountain root delamination under this orogenic belt led to post collisional crustal extension at the end of the triassic forming a series of rift basins on this continental margin arc significant potential for vhms deposits occurs in the submarine volcanic districts of the job mesozoic vhms deposits occur in the post collisional extension environment and cluster in the late triassic rift basins

geochemistry mineralogy and mineral chemistry of the welatam cu mo bi au prospect northeast myanmar abstract the welatam prospect located in kachin state northeast myanmar is the first discovered bismuth gold locality within the tengchong lianghe tengliang metallogenic district two mineralization types identified in this area are related to three hydrothermal events the massive sulfide mineralization was formed during the hydrothermal activities of stage i and ii producing mainly iron sulfides e g pyrrhotite chalcopyrite pyrite arsenopyrite whereas the activity of stage iii resulted in quartz molybdenite mineralization which is characterized by the deposition of molybdenite galena and bi te au bearing phases the bi mineral assemblages suggest that at stage iii the prevailing temperatures were above 271 c fluid rock interaction that changed the ph fo2 fs2 and in particular temperature in hydrothermal fluids is important in causing the precipitation of liquid bismuth from bi3 the high correlation between bi and au r 0 782 demonstrates that liquid bismuth may have played a crucial role in gold enrichment here bi au bearing minerals commonly precipitate along the cleavages of molybdenite forming a distinctive mineral assemblage it may indicate that the cleavages besides providing spaces for the precipitation of liquid bismuth create local chemical conditions e g reducing and catalytic surfaces favorable for bi melt to scavenge au from ambient fluid the abundant bi minerals metal association e g cu bi mo au te w the restricted 34s values 7 3 to 1 9 of sulfides and the proximity with the welatam monzogranites suggest a magmatic contribution to the ore forming fluids

a mafic intrusion of arc affinity in a post orogenic extensional setting a case study from ganluogou gabbro in the northern yidun arc belt eastern tibetan plateau abstract generally arc related or subduction related mafic magmas are formed during or slightly postdate subduction and characterized by depletion in high field strength elements hfses relative to the large ion lithophile elements liles and light rare earth elements lrees combining with mineral chemistry and sr nd isotopes these geochemical characteristics were usually used to define an arc setting especially for some ancient arcs that had been strongly modified by later tectonic activities however we report an exceptional case from the northern part of the triassic yidun arc belt eastern tibetan plateau the ganluogou gabbro 152 ma occurs as several intrusive bodies its mineral assemblage is olivine chrysolite plagioclase anorthite clinopyroxene diopside amphibole edenite and pargasite and phlogopite whole rock geochemistry shows low sio 2 42 87 46 99 wt total rear earth elements ree 22 8 28 4 ppm na 2 o k 2 o 0 92 1 34 wt and high al 2 o 3 mgo and feo contents it has small variations of initial 87 sr 86 sr 87 sr 86 sr i 0 7053 0 7055 and e nd t values 4 8 to 1 8 all the samples exhibit enrichment in liles including th and u but strongly depleted in hfses including nb ta zr and hf for the mineral chemistry there are two type amphiboles amp i show higher v sc cr sr nb and zr contents but lower th and u contents than those of amp ii their ree patterns range from convex shape without eu anomaly to lree enriched pattern with weak positive eu anomaly we suggest that amp i was crystallized from a liquid that was mainly buffered by olivine clinopyroxene and plagioclase while amp ii crystallized from later melt that was mainly buffered by olivine based on clinopyroxene chemistry compositions of coexisting olivine and plagioclase and whole rock sr nd isotopes the parental magma of the ganluogou gabbro is interpreted as a tholeiitic arc affinity magma which might be derived from an n morb mantle that had been metasomatised by slab derived melts in the late triassic 237 206 ma thus the ganluogou gabbro provides an example that magmas exhibiting arc affinity could in fact be formed in a post orogenic extensional setting

late cretaceous granitic intrusions and associated deposits in the yidun arc of the eastern tibetan plateau abstract the yidun arc is an important tectonic unit and polymetallic metallogenic belt in the sanjiang tectono magmatic belt in which many cretaceous 138 75 ma granites and associated polymetallic deposits are distributed along a nw trending belt the queershan cuomolong rongyicuo and genie granitic intrusions and the associated sn pb zn ag polymetallic deposits are distributed in the changtai and xiangcheng arcs whereas the xiuwacu relin hongshan and tongchanggou granitic intrusions and the associated cu mo w deposits are mainly distributed in the geza arc this study presents new zircon u pb hf o isotopic data for the queershan cuomolong rongyicuo genie xiuwacu and tongchanggou granitic intrusions combined with the structural analysis of the xiuwacu granitic complex to discuss the differences in the petrogenesis and metallogenesis of these granitic intrusions as well as the geodynamic processes that controlled the formation of the late cretaceous intrusions and related deposits hf o isotopic characteristics indicate that the highly fractionated granites hfg in the changtai and xiangcheng arcs were mainly derived from the partial melting of metasedimentary crustal materials with a minor input from mantle components while the i type granites ig in the geza arc were predominantly derived from the partial melting of ancient lower crustal material the spatial distributions of the different types of deposits in the yidun arc were probably controlled by the magma sources reduced magmas produced by the partial melting of the sedimentary crust in the changtai and xiangcheng arcs are favorable for w sn pb and zn mineralization whereas oxidized magmas produced by the partial melting of the lower crust in the geza arc are conducive to the enrichment of cu au and mo the geochronological data indicate that the emplacement ages of the late cretaceous granites in the yidun arc gradually decrease from north to south ranging from 106 to 73 ma reflecting the southward lateral tectonic migration the structural analysis of the xiuwacu w mo deposit in combination with previous studies demonstrated that the late cretaceous granites in the yidun arc were likely formed in a regional extensional setting which was probably related to the slab break off of the bangong nujiang oceanic slab or the subduction of the yarlung zangbo oceanic slab

zircon u pb geochronology and elemental and sr nd hf isotopic geochemistry of the daocheng granitic pluton from the yidun arc sw china abstract the garze litang suture zone located in the eastern part of the tethyan tectonic domain is notable for widespread late triassic granitic plutons which are genetically associated with the evolution of the paleo tethys ocean the daocheng granitic pluton in the eastern yidun arc sw china is located in the middle of the garze litang suture zone and has an outcrop area of 2800 km 2 in the present study we report zircon u pb ages and elemental and sr nd hf isotopic data for the daocheng granitic intrusion secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry u pb analyses on zircons yield consistent ages of ca 216 ma for three samples from the pluton all the daocheng granitic rocks are enriched in si sio 2 68 1 76 4 and large ion lithophile elements but depleted in high field strength elements e g nb ta and ti mineralogical and geochemical features indicate that these are high k and calc alkaline and i type granites they are characterized by relatively variable initial 87 sr 86 sr ratios 0 7059 0 7102 negative e nd t values 5 7 to 7 8 wide ranging e hf t values 9 8 to 3 4 and two stage hf model ages of 1 04 to 1 88 ga these isotopic signatures indicate that the source for the daocheng granite was probably derived from partial melting of a late paleoproterozoic to early mesoproterozoic mafic intermediate lower crust with a variably minor addition

the lithospheric architecture of two subterranes in the eastern yidun terrane east tethys insights from hf nd isotopic mapping abstract a long standing controversy exists regarding the tectonic division lithospheric architecture and evolution of the eastern yidun terrane in the late triassic a compilation of geochronological geochemical and isotopic data 91 whole rock nd and 413 laser points of zircon hf for volcanic and intrusive rocks across the entire eastern yidun terrane has allowed for a detailed investigation into its lithospheric architecture two subterranes were identified using hf nd isotopic mapping they include a high hf t 3 0 and nd t 3 5 domain constrained in the southern yidun terrane syt and a low hf t

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

stochastic model for the long term transport of stored sediment in a river channel we develop a stochastic model for the transport of stored sediment down a river channel the model is based on probabilities of transition of particles among four different sediment storage reservoirs called active often mobilized semiactive inactive and stable hardly ever mobilized the probabilities are derived from computed sediment residence times two aspects of sediment storage are investigated flushing times of sediment out of a storage reservoir and changes in the quantity of sediment stored in different reservoirs due to seasonal sediment transport into and out of a reach we apply the model to redwood creek a gravel bed river in northern california although the redwood creek data set is incomplete the application serves as an example of the sorts of analyses that can be done with the method the application also provides insights into the sediment storage process sediment flushing times are highly dependent on the degree of interaction of the stable reservoir with the more mobile sediment reservoirs the most infrequent and highest intensity storm events which mobilize the stable reservoir are responsible for the long term shifts in sediment storage turnover times of channel sediment in all but the stable reservoir are on the order of 750 years suggesting this is all the time needed for thorough interchange between these sediment compartments and cycling of most sediment particles from the initial reservoir to the ocean finally the markov model has adequately characterized sediment storage changes in redwood creek for 1947 1982 especially for the active reservoir the model replicates field observation of the passage of a slug of sediment through the active reservoir of the middle reach of redwood creek in the 18 years following a major storm in 1964 that introduced large quantities of landslide debris to the channel

vertical mixing of coarse particles in gravel bed rivers a kinematic model burial of transported material in gravel bed rivers was examined using several hundred magnetically tagged particles burial depth of individual particles varies with no simple relation to particle size distributions of burial depth of particles were examined by considering observed burial depth of individual size groups of all mobile particles and of all tagged particles including static ones simple single peak flow events yielded exponential distributions of burial depth of mobile particles distributions with secondary peaks were obtained from large and multipeak events season long results were skew peaked with a tendency toward uniformity an m layer model is developed to account for the variation of frequency of burial depth of particles based on the assumptions that the burial depth of particles in a simple event is exponentially distributed and the proportion of particles which change vertical position from a given layer is constant from event to event the model is elaborated for varying mixing rates varying scour depths and variable behavior of different size classes after many events the material is uniformly distributed throughout all layers in conformity with field experience

henty a shallow water gold rich volcanogenic massive sulfide deposit in western tasmania the mount read volcanics of western tasmania host a number of polymetallic volcanogenic massive sulfide deposits a cluster of disseminated cu au deposits at mount lyell and a high grade gold deposit avg grade 27 ppm au at henty the henty deposit occurs at the base of the tyndall group a sequence of rhyolite lavas and crystal rich volcaniclastics fossiliferous sediments and welded ignimbrites within this group are indicative of a local shallow water environment mineralization occurs in a conformable package of altered rocks in the footwall of a major fault the host rocks were strongly deformed during a later compressional event the deposit has a distinct asymmetry in its alteration and metal distribution an exhalite unit is zoned outward from massive pyrite with minor lenses of massive sulfide to massive calcite with red jasper to a chlorite calcite rock gold occurs with pyrite chalcopyrite and galena in late fractures in an intensely silicified zone in the footwall of the massive pyrite this zone is surrounded by silica sericite pyrite altered rocks with disseminated base metals during the deformation the silicified rocks were repeatedly fractured whereas the sericite rich rocks became high strain zones pressure solution of sulfides enhanced gold transport into late brittle fractures high gold values are confined to the footwall of proximal parts of the exhalite indicating that gold was introduced during the volcanogenic massive sulfide event and that remobilization was a localized process

continental underplating model for the rise of the tibetan plateau abstract subduction of continental lithosphere entrained in an oceanic plate for distances of several hundred kilometers can lead to continental underplating whereby the continental crust with or without its lithospheric mantle is detached at depth from the main part of the sinking slab and rises buoyantly beneath the overriding plate the rising continental material causes first extension in the overriding plate as the asthenosphere flows laterally and later rapid isostatic uplift when it reaches the base of the overriding lithosphere this continental underplating model is applied to the geology of the tibetan region and the following stages are identified 100 ma to 50 ma oceanic subduction leading to continental collision 50 ma to 20 ma pause in convergence with possible delamination of indian crust 20 ma to 5 ma continental subduction initially at an angle of 30 of indian lithosphere along the main central thrust 5 ma to 2 ma rise of the continental lithosphere displacing the asthenosphere beneath tibet and causing widespread graben formation 2 ma to present contact between the underplating indian continental lithosphere and the overlying asian crust leading to rapid rise of the surface altitude by 3 4 km present day convergence between india and tibet albeit at a rate much less than the total india eurasia convergence continues as continental underthrusting

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

metallogenic model of the jinchang au ni deposit in the ailaoshan belt sw china determined on the basis of pyrite trace element contents in situ sulfur isotope composition and pge geochemistry abstract the ailaoshan metallogenic belt in southwestern china contains numerous shear zone related au deposits with au reserves greater than 200 tonnes however the source of ore forming fluids and metals is controversial hampering the construction of genetic models in this study we selected the jinchang au ni deposit in the northern segment of the ailaoshan belt for detailed investigation of pyrite chemistry and in situ sulfur isotope compositions using laser ablation inductively coupled plasma mass spectrometry la icp ms the petrographic and pyrite chemistry analyses revealed four types of hydrothermal pyrite py1 pyrite is euhedral to subhedral and has in situ sulfur isotope 34s values of 5 30 to 6 26 median 2 93 and low concentrations of au ni as sb cu zn pb and ag py1 is interpreted to have formed during the early hydrothermal stage py2 pyrite is subhedral to anhedral and porous with variable size although py2 and py3 show different textural relationships we conclude that both of them formed during the intermediate hydrothermal stage as evidenced by similar sulfur isotope compositions and trace element contents and common intergrowth textures py2 and py3 pyrite have in situ 34s values ranging from 11 6 to 1 29 median 4 45 and relatively elevated concentrations of au ni as sb cu zn pb and ag in py2 and py3 pyrite ni concentrations correlate with co concentration whereas au exhibits moderate positive correlations with ni co and as indicating that au ni and other metals were predominantly sourced from the jinchang ultramafic rocks py4 pyrite is euhedral in shape and has relatively low in situ 34s values of 23 5 to 4 34 median 8 33 the metal concentrations in py4 pyrite are lower than those in py2 and py3 pyrite in general the metal concentrations in the different pyrite populations display systematic changes with low levels in py1 higher levels in py2 andpy3 and low levels again in py4 the average total platinum group element pge concentration of the jinchang ni bearing ultramafic rocks is 26 3 ppb similar to the average value of the primitive mantle of 22 0 ppb the au ni ores from the jinchang deposit have an average pd pt ratio of 5 98 similar to that of hydrothermal ni ores but higher than that of typical magmatic ni ores in contrast the jinchang ultramafic rocks have low pd pt ratios between 0 57 and 1 13 suggesting that the pges in the jinchang intrusion are of magmatic origin similarly the rh ir ratios of au ni ores are consistent with those of hydrothermal ni ores but differ from those of magmatic ni ores the pyrite chemistry in situ sulfur isotope compositions and pge geochemistry suggest that the ore forming fluids and metals associated with the jinchang au ni deposit were dominantly derived from the jinchang ultramafic intrusion mesozoic felsic magmatism or cenozoic regional strike slip activity may have triggered migration of the ore forming fluids leaching of metals from the jinchang intrusion and precipitation of these metals at the boundary between the intrusions and carbonaceous rocks

petrogenesis of eocene mineralized porphyry in bijiashan eastern margin of tibet plateau constraints from geochronology geochemistry and hf isotopes abstract the ailaoshan jinshajiang porphyry belt located in the sanjiang area of eastern tibetan plateau is one of the major polymetallic metallogenic belts in china however the nature and genesis of magmatic intrusions associated with the porphyry copper mineralization in this belt remain contentious here we focus on the bijiashan deposit one of the large scale porphyry copper deposits in this area to gain insights on the host rock petrogenetic mechanism tectonic setting based on geochemistry zircon u pb geochronology and lu hf isotopic compositions zircon u pb dating of the ore hosting porphyry yielded an age of 35 6 0 2 ma the major elements of the porphyry show wide range in sio2 58 33 70 high k2o 2 83 8 85 and na2o k2o mostly 8 and moderate range in a cnk 0 56 1 17 our data suggest that the porphyry belongs to high kcalc alkaline alkaline and metaluminous peraluminous series the trace elements are characterized by enrichment in k rb ba la and nd but depletion in ta nb p and ti and enrichment in lree but depletion in hree with lree hree of 9 78 20 10 the main intrusion associated with mineralization corresponds to alkali richa type granitoid with high tfeo 0 49 3 4 low na2o k2o 0 23 1 62 and high 1000 ga al 2 17 2 64 except 1 57 and right declinedree patterns however some of the geochemical features also are consitent with the typical characteristics of c adakite rocks including high contents of al2o3 13 49 16 12 and sr 400 ppm lower mgo mostly

slope induced changes in channel character along a gravel bed stream the allt dubhaig scotland changes in channel character along a small river in the scottish highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0 02 to o ooo15 because of local baselevel control this decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed the channel pattern alters progressively rather than abruptly in the sequence 1 near braided 2 meandering with active point bar chutes 3 meandering with active outer bank talweg 4 stable equiwidth sinuous the changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical cdncepts than by purely empirical discriminant or trend equations measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload it is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions are typical of many streams in mountainous areas and can be understood in terms of slope induced changes in hydraulic properties

delamination in collisional orogens during continental collision the weight of the downgoing slab may lead to extensional shearing in the descending plate permitting separation of the downdip dense oceanic lithosphere from the adjacent lighter continental lithospher separation may occur by means of a lithosphere penetrating normal sense shear zone by means of pure shear necking of the lithosphere or by some combination of these mechanisms during separation the continental crust attached to the lower plate may undergo an episode of extensional tectonics the proximity of asthenosphere to crust may result in syntectonic regional metamorphism and plutonism if the continents continue to converge following delamination a compressive tectonic regime will be reestablished in the crust the subsequent cooling of asthenosphere at the base of the crust may lead to the establishment of a continuous flat moho the likely imbrication of crustal and mantle lithologies during delamination and during the subsequent compressive tectonic regime as well as underplating associated with syntectonic plutonism may account for the seismic complexities observed at moho depths beneath some mountain belts

a special issue devoted to porphyry copper deposits of northern chile chile is known worldwide as the site of one of the largest copper concentrations on earth a total resource including production of about 400 million tons mt of fine copper has been identified in 50 porphyry copper deposits and numerous prospects fig 1 considering 10 mt of contained fine copper as a minimum tonnage to classify a porphyry copper deposit as a giant ore deposit the chilean cordillera contains nine of the 16 giant porphyries along the circum pacific belt among them are the three largest of all el teniente rio blanco los bronces and chuquicamata fig 1 all containing resources plus production of more than 50 mt of fine copper currently chile annually produces about 4 6 mt of fine copper that represents about 37 percent of the world production this enormous geologic potential has triggered numerous international mining companies to concentrate their exploration efforts in the central andes with emphasis in chile during the past 25 years exploration expenditures have surpassed a figure on the order of us 2 billion as a result a total of 76 copper and gold discoveries have been made 24 of which are already in production cabello 2000 among them the most relevant discoveries are the porphyries at la escondida escondida norte zaldivar rosario and ujina in the collahuasi mining district quebrada blanca lomas bayas and in the last 5 years spence and gaby sur the presence of such a significant number and large size of copper porphyries intrigued several generations of researchers during the twentieth century the ongoing exploration efforts have enhanced the interest in understanding the andean geological evolution and metallogenesis the geological processes that are common factors in controlling the emplacement of these orebodies have been the subject of research by numerous individuals in chile and elsewhere the support of mining companies has been

geochronology and isotope analysis of the late paleozoic to mesozoic granitoids from northeastern vietnam and implications for the evolution of the south china block abstract in northeastern vietnam late paleozoic and permo triassic granitic plutons are widespread but their tectonic significance is controversial in order to understand the regional magmatism and crustal evolution processes of the south china block scb this study reports integrated in situ u pb hf o and sr nd isotope analyses of granitic rocks from five plutons in northeastern vietnam zircon sims u pb ages of six granitic samples cluster around in two groups 255 228 ma and 90 ma bulk rock end t ranges from 11 to 9 7 suggesting that continental crust materials were involved in their granitic genesis in situ zircon hf o isotopic measurements for the granitic samples yield a mixing trend between the mantle and supracrustal derived melts it is suggested that the granitic rocks were formed by re melting of the continental crust these new data are compared with the paleozoic and mesozoic granitic rocks of south china we argue that northeastern vietnam belongs to the south china block though still speculated an ophiolitic suture between ne vietnam and south china so called babu ophiolite appears unlikely the late paleozoic to mesozoic magmatism in the research area provides new insights for the magmatic evolution of the south china block

modelling sediment transport as a moving wave the transfer and deposition of mining waste abstract the movement of slugs of bedload from a discrete input point down a river has proved difficult to model using conventional finite difference formulations of equations of motion a model is proposed which makes explicit allowance for the mean sediment velocity and through a dispersion coefficient the distribution of sediment velocity about the mean a second comparative model uses the normal mass conservation or sediment transport continuity approach the models have been tested over a 43 month period using data from seven monitored cross sections of the kawerong river on bougainville island papua new guinea a system which receives waste from a large copper mine the dispersion model performs considerably better than the mass conservation model

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

geochemistry of the cambrian volcanic hosted massive sulfide rich mount read volcanics tasmania and some tectonic implications the cambrian mount read volcanics belt in western tasmania hosts five major gold rich massive sulfide deposits and remains the focus of intense exploration activity and geologic research a geochemical study of least altered lavas and shallow intrusions with emphasis on basaltic to andesitic compositions was carried out to determine the primary magmatic affinities and tectonic setting of eruption of the mount read volcanics to aid in internal correlations within the belt and to provide starting material estimates for mineralization related alteration studies three calc alkaline suites one extending to shoshonitic compositions and two tholeitiic suites have been distinguished within the mount read belt suite i is voluminous and includes the eastern sequence central volcanic complex tyndall group the intrusive quartz feld spar porphyries and granitoids and the andesitic lavas of the que hellyer footwall sequence suite i andesites are transitional medium to high k calc alkaline rocks la yb n 5 12 avg 8 1 and are the least light ree enriched calc alkaline lavas in the mount read volcanics suite ii comprises intrusive and extrusive often hornblende porphyritic andesites and dacites mainly from the upper part of the southern central volcanic complex they are more p 2 o 5 and light ree enriched la yb n 10 26 avg 16 7 than suite i and have high k calc alkaline affinities suite iii includes basaltic and andesitic lavas from the que hellyer hanging wall sequence in the northern part of the belt the lynch creek basalts near queenstown and intrusive basalts in the howards plains area northwest of queenstown suite iii rocks show a striking compositional range from low tio 2 0 4 0 5 low p 2 o 5 0 1 basalts with la yb n values from 8 to 12 and almost flat heavy ree patterns to low tio 2 0 4 0 8 but strongly to exceptionally p 2 o 5 and light ree enriched basalts with up to 350 times chondritic la and la yb n values up to 34 the latter are regarded as shoshonites tholeiitic pillow basalts of the henty fault wedge and the closely related dikes of the henty dike swarm constitute suite iv these have tio 2 contents from 1 0 to 1 6 percent very low nb contents 3 ppm and only slightly light ree enriched ree patterns la yb n 1 4 3 4 they are considered to be most similar to suprasubduction zone basalts erupted during the early phase of arc splitting and back arc basin development and indicate a period of tension and rifting of the mount read belt in post central volcanic complex but pre tyndall group time suite v is constituted by the miners ridge basalts and includes low tio 2 0 7 basalts with strong light ree depletion la yb n 0 5 and higher tio 2 to 2 6 lavas with only slight light ree depletion la yb n 0 9 suite v basalts are tentatively correlated with rift tholeiite sequences associated with the crimson creek formation and therefore are regarded as part of the pre mount read volcanics basement the three calc alkaline suites occur in a general stratigraphic order with suites i and ii being more or less coeval near queenstown they indicate a magmatic evolution from transitional medium to high k rocks through high k rocks to strongly enriched shoshonitic rocks closest modern analogues are postcollisional volcanics in regions of arc continent collision e g east papua and the roman province the occurrence of boninite derived chromites probably derived from the allochthonous mafic ultramafic complexes outcropping just west of the mount read belt in two sedimentary units within the mount read volcanics sequence below suite iii basalts supports a postcollisional origin for at least the major part of the mount read volcanics other similar postcollisional sequences particularly if formed in a submarine setting must be considered highly prospective for vhms deposits

characteristics and genesis of gangdese porphyry copper deposits in the southern tibetan plateau preliminary geochemical and geochronological results porphyry type cu mo au deposits have been discovered along the gangdese magmatic arc in the southern tibetan plateau extensive field investigations and systematic studies of geochemistry s pb isotopic tracing together with re os and 40ar 39ar isotopic dating indicate that the mineralisation of the copper belt is genetically related to emplacement of late orogenic granitic porphyries during the post collisional crustal relaxation period of the late himalayan epoch these porphyries are petrochemically k enriched and belong to shoshonitic to high k calc alkaline series they display enrichment of large ion lithophile elements lile rb k u th sr pb and depletion of high field strength elements hfse nb ta ti and the heavy rare earth elements hree and y without eu anomalies these characteristics demonstrate that subduction played a dominant role in their petrogenesis and residual garnet was left in the magma sources pb isotope data show a linear correlation in the plumbotectonic framework diagram ranging from orogenic pb in the eastern segment of the copper belt to mantle pb in the western segment these constitute a mixing line of the indian oceanic morb with indian oceanic sediments and suggest that the porphyry magmas were dominantly derived from partial melting of subducted oceanic crusts mixed with a minor quantity of sediments and mantle wedge components the gangdese porphyry copper polymetallic belt has alteration characteristics and zonation typical of porphyry type copper deposits which include potassic alteration k feldspathisation and biotitisation silicification sericitisation and propylitisation mineralisation mainly occurs in strongly altered granitic cataclasite at the exo contact with veinlet disseminated textures the porphyries themselves are weakly mineralised with disseminated pyrite and chalcopyrite the copper deposits contain simple ore mineral associations consisting of chalcopyrite pyrite bornite molybdenite sphalerite and oxidised minerals of malachite covellite and molybdite during supergene oxidation primary ores underwent secondary enrichment to form economic orebodies with cu grade ranging from 1 to 5 ore sulphides of the copper belt display s and pb isotopic compositions identical to the ore bearing porphyries their 34s values vary between 3 8 and 2 4 and are typical of mantle sulphur the 206pb 204pb 207pb 204pb and 208pb 204pb ratios vary in the ranges 18 106 to 18 752 15 501 to 15 638 and 37 394 to 39 058 respectively and yielded radiogenetic lead enriched signatures twelve molybdenite samples from the copper belt yielded isochron ages of 14 76 0 22 ma and 13 99 0 16 ma for the nanmu and chongjiang deposits and model ages of 13 5 to 13 6 ma for the lakang e deposit meanwhile 40ar 39ar isotopic dating of two biotite phenocrysts from the chongjiang and lakang e deposits give plateau ages of 13 5 1 0 ma and 13 42 0 10 ma respectively during the geodynamic evolution of the gangdese collision orogenic belt intrusion of the ore bearing porphyries took place just before the rapid uplift and e w extension of the southern plateau and the ore forming process may have occurred simultaneously with the uplift and extension 14 0 1 ma

meso scale catchment sediment budgets combining field surveys and modeling in the dragonja catchment southwest slovenia in this paper we present a methodology to construct a sediment budget for meso scale catchments we combine extensive field surveys and expert knowledge of the catchment with a sediment delivery model the meso scale mediterranean drainage basin of the dragonja 91 km2 southwest slovenia was chosen as case study area during the field surveys sheet wash was observed on sloping agricultural fields during numerous rainfall events which was found to be the main source of sediment with the sediment yield model watem sedem the estimated net erosion on the hillslopes 4 1 t ha 1 y 1 91 of inputs the second source bank erosion 4 2 0 25 t ha 1 y 1 was monitored during several years with erosion pins and photogrammetric techniques the last source channel incision was derived from geomorphological mapping and lichenomery and provided 3 8 0 17 t ha 1 y 1 of the sediment input the river transports its suspended sediment mainly during high flow events sampled with automated water samplers about 27 1 2 t ha 1 y 1 of the sediment delivered to the channel is deposited on floodplains and low terraces downstream estimated with geomorphological mapping coring and cesium 137 measurements the sediment transported as bedload disintegrates during transport to the outlet due to the softness of the bedrock material as a result the river carries no bedload when it reaches the sea the results imply a build up of sediment in the valleys catchment however extreme flood events may flush large amounts of sediment stored in the lower parts of the system geomorphological evidence exists in the catchment that such high magnitude low frequency events have happened in the past

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

right lateral shear and rotation as the explanation for strike slip faulting in eastern tibet the convergence of two continents can be accommodated by crustal thickening and by lateral transport of crust out of the path of the converging continents1 3 the principal features suggesting that lateral transport is important are major strike slip faults striking roughly orthogonally to the orientation of convergence between the continents displacement on such faults is imagined to allow lateral transport of material with respect to the converging continents possibly accounting for a large fraction of the convergence between the two continents the most spectacular example of such strike slip faulting is in the eastern part of the tibetan plateau where three major left lateral faults with slip rates of 10 mm yr 1 and several smaller roughly parallel faults dominate the regional strain field2 3 cobbold and davy4 suggested that these faults may be rotating in a clockwise fashion here we put bounds on that rate of rotation and conclude that the image of lateral transport on such faults2 known also as continental escape extrusion or expulsion is an illusion and that instead the left lateral slip on east striking planes in eastern tibet is a manifestation of north striking right lateral simple shear if this conclusion is correct the east striking left lateral faults and the crustal blocks between them are rotating clockwise at 1 2 myr 1 the east west dimension of eastern tibet is shortening at 10 20 mm yr 1 and little material is moving eastward out of india s path into eurasia by left lateral simple shear

sediment residence time in alluvial storage of black marl badlands abstract the aim of this study is to estimate the sediment residence time in the stream network of two small headwater catchments laval and moulin characterized by a badlands landscape entrenched into jurassic black marls of the southern french prealps the method is based on an intensive field survey of the alluvial storage along the main stream reaches from which a scaling law between the average thickness of alluvial deposits and their width was established in order to predict the volume of alluvial deposits in the entire stream network to complete this approach bedload sediment yield monitored over the last 30 years with topographic surveying of sediment retention basins are used the assessment of sediment residence time is performed according to a steady state assumption validated by the long term dynamic equilibrium of bedload sediment yields the results highlighted very close values of residence time between the catchments around 3 years despite a one order of magnitude difference in drainage area it is shown that the rate of increase of alluvial storage with drainage area is the same as for sediment yield this is likely attributed to the high degree of confinement of the stream network which prevent the formation of a floodplain or large internal alluvial fans implications of these results for the prediction of the effects of bioengineering works in controlling erosion are discussed

observations of flow and sediment entrainment on a large gravel bed river constant discharge reservoir releases on the trinity river california provide an unusual opportunity to unambiguously relate flow and gravel entrainment on a large gravel bed river bed shear stress 0 was estimated using local observations of depth averaged velocity gravel entrainment was measured using large tracer gravel installations lateral variability of 0 is large even for straight channels with simple trough like geometry no simple relation exists between local and cross section mean values of 0 fine grains less than 8 mm 20 30 of the bed material are transported at lower discharges than coarse grains scour to the base of the bed surface layer occurs at a dimensionless shear stress g 0 035 for g formed using local 0 and the median grain size of the gravel portion of the bed the dimensionless reference transport rate w 0 002 often used as a surrogate for the threshold of grain motion occurs at nearly the same g at smaller g entrainment and transport rates decrease rapidly becoming vanishingly small at g 0 031 even at very small gravel transport rates all sizes are transported although the coarsest sizes are in a state of partial transport in which only a portion of the exposed grains are entrained both entrainment and cumulative transport observations suggest that maximum scour depth for plane bed transport is slightly less than twice the surface layer thickness

tracer pebble movement along a concave river profile virtual velocity in relation to grain size and shear stress over 1400 tracer pebbles 16 256 mm in diameter were tracked for 2 years in six reaches of allt dubhaig scotland a small gravel bed river along which shear stress and bed surface grain size decrease toward a local base level pebble movement was size selective both within and between reaches within reaches the decrease in mean travel distance with increasing grain size is strongest in the coarse tail of the size distribution particle shape has a minor secondary effect a nondimensional grain velocity averaged over the duration of competent flow is used to compare different size classes and reaches over 90 of its variance is explained by relative grain size and reach shields stress the pattern of size selectivity is consistent with single event tracer results elsewhere bedload trap data from our distal reach and the concept of partial mobility it provides a mechanism for strong downstream fining by selective transport and deposition along rivers in which stress declines toward base level the nondimensional prediction equation for grain velocity may be of use in other rivers but requires testing

new zircon fission track analysis constraints on tectonic mineralization epochs in the ganzi litang gold belt eastern qinghai tibet plateau abstract the ganzi litang gold belt as a part of the sanjiang tethys orogen is located between the yidun block and songpan ganzi block terrane in the eastern qinghai tibetan plateau and experienced oceanic slab subduction continent arc collision and intracontinental convergence since the indosinian orogeny a series of gold ore deposits have been found within the region this paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track ft thermochronology a total of 15 zircon ft analysis results were obtained that can be divided into four age groups 217 213 ma 190 160 ma 155 93 ma and 72 67 ma representing four distinct episodes of gold mineralization of which the middle two episodes predominate eruption of the auriferous volcanic rocks that comprise the belt started at 217 213 ma when the ganzi litang meso tethys ocean began to subduct the mineralization episode at 190 160 ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional convergence of the ganzi litang belt finally the episodes at 155 93 ma and 72 67 ma are respectively related to the closing times of the bangong nujiang and yarlung zangbu oceans corresponding to tectonic quiet episodes

gully erosion and sediment production te weraroa stream new zealand conversion to pasture early in the twentieth century was ameliorated by reforestation that commenced in 1962 estimates of sediment production were made using the change in gully area observed in sequential aerial photographs channel storage was assessed from stream cross section surveys at its peak gully erosion affected 6 of the total catchment area the amount of sediment contributed from gullies declined by 62 as the forest became established but of the 28 7 mt of sediment generated by gully erosion between 1950 and 1988 48 was stored in the channel along the lower 8 km of te weraroa stream even if the amount of sediment generated by gully erosion continues to decline it likely will be many decades before the gravel is released from storage index terms 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 1878 hydrology water energy interactions keywords channel storage gully erosion sediment production citation gomez b k banbury m marden n a trustrum d h peacock and p j hoskin gully erosion and sediment production te weraroa stream new zealand water resour res 39 7 1187 doi 10 1029 2002wr001342 2003

formation and evacuation of a large gravel bar deposited during a major flood in a mediterranean ephemeral stream nahal me arot nw israel abstract an unusual 240 mm rainstorm and a consequent major flood peak discharge 110 m 3 s 1 with an estimated recurrence interval of about 50 years occurred on dec 31 1998 in nahal me arot an ungauged 25 km 2 coastal ephemeral stream in mt carmel nw israel the flood caused morphological modifications along the channel including intensive stripping of the channel bed and floodplain along several segments and deposition of large gravel bars downstream of these segments one of such segments served as a study reach composed of a massive 1270 m 3 coarse 200 m long gravel bar formed downstream of a segment 150 m long that was deeply scoured the study reach was carefully mapped cross sections and driftwood lines allowed the calculation of the hydraulic parameters and peak flow using the slope area method the bar s sedimentological characteristics such as surface and substrate texture and stratigraphy were studied in detail using a survey of 15 pits the initial recovery of the channel started when dense low shrub vegetation re stabilized along the affected reaches a year later two smaller floods 3 and 4 years later evacuated and reworked the sediment until it lost most of its volume the study suggests that the flood s large impact and disturbance was local short lived and the channel almost returned to its pre flood state within about 4 years