zircon u pb geochronological and hf isotopic constraints on petrogenesis of late mesozoic intrusions in the southeast hubei province middle lower yangtze river belt mlyrb east china abstract during the late mesozoic extensive magmatism and associated ore deposits were developed in the southeast hubei province middle lower yangtze river metallogenic belt mlyrb east china to understand the petrogenesis of the intrusions in the area we performed in situ zircon u pb and hf isotopic analyses on 14 samples from the fengshangdong stock and from the echeng tieshan wangbaoshan jinshandian and yangxin batholiths three major suites of intrusive rocks are recognized in the southeast hubei province 1 141 146 ma granodiorite and granite porphyries associated with 143 144 ma porphyry skarn cu mo deposits have enriched radiogenic hf isotopic compositions ehf t 9 5 to 1 6 comparable to those of cretaceous pyroxene diorites trachyandesites and basalts ehf t 8 9 to 1 3 in the mlyrb which were derived from an enriched lithospheric mantle 2 voluminous 136 143 ma gabbros diorites and quartz diorites associated with 137 144 ma skarn cu fe fe cu and au cu deposits have variable hf isotopic compositions ehf t 19 1 to 5 4 indicating an origin via the hybridization of enriched mantle derived mafic magma and variable amounts of ancient lower crustal components 3 127 133 ma diorites quartz diorites and granites associated with 132 133 ma skarn fe deposits characterized by a wide range of ehf t values 28 2 to 6 4 suggest the assimilation of various ancient lower crustal materials by enriched mantle derived basaltic magma the intrusions of suites 1 and 2 are characterized by high sr contents 329 2087 ppm and high sr yb 36 1710 and la yb n ratios 17 6 172 but low yb contents 0 45 1 82 ppm and do not show negative eu anomalies eu 0 74 1 4 the intrusions have radiogenic sr nd isotopic compositions end t 10 0 to 3 4 and 87 sr 86 sr i 0 7054 0 7084 compared with the intrusions of suites 1 and 2 rocks of suite 3 have relatively low sr contents 60 5 327 ppm and low sr yb 33 0 315 and la yb n ratios 2 28 30 0 but relatively high yb contents 1 04 5 17 ppm and significant negative eu anomalies eu 0 22 0 73 the rocks of suite 3 are characterized by a wide range of radiogenic sr nd isotopes with end t values of 12 5 to 4 9 and 87 sr 86 sr i 0 7057 0 7085 the proposed magma sources combined with the geochemical and sr nd isotopic differences between these three suites of intrusive rocks indicate that late mesozoic magmatic activity in the southeast hubei province mlyrb was associated with lithospheric thinning induced by asthenospheric upwelling at that time

metallogeny of the handagai skarn fe cu deposit northern great xing an range ne china constraints on fluid inclusions and skarn genesis abstract the newly discovered handagai skarn fe cu deposit is located in the northern great xing an range of ne china and is hosted by the ordovician luohe formation the orebodies that form the deposit are generally concordant with the bedding within these sediments and are spatially related to areas of skarn development the fe cu mineralization in this area records four stages of paragenesis namely prograde skarn retrograde skarn quartz sulfide and quartz carbonate stages the handagai deposit is a calcic skarn that is dominated by an andradite diopside epidote actinolite assemblage the mineralogy and geochemistry of the skarn indicate that it formed from a hydrothermal fluid that altered the carbonate units in this area to a garnet and42 95grs4 53 and pyroxene di71 78hd22 29jo0 2 bearing skarn the epidote within the skarn has an epidote end member composition with the chlorite in the skarn dominantly fe rich indicating that these minerals formed in an fe rich environment the petrographic microthermometric and raman spectroscopic analysis of fluid inclusions within garnet epidote actinolite quartz and calcite precipitated at different stages of formation of the handagai deposit indicate that mineralization related fluid inclusions are either liquid rich two phase h2o nacl type i gas rich two phase h2o nacl type ii three phase liquid vapor solid h2o nacl type iii or co2 h2o nacl inclusions type iv the early stages of mineralization are associated with all four types of inclusion whereas the later stages of mineralization are only associated with type i and ii inclusions inclusion homogenization temperatures vary between the four stages of mineralization 370 c 530 c and 600 c 210 c 290 c 190 c 270 c and 150 c 230 c from early to late respectively with salinities also varying between the earlier and later stages of mineralization 11 18 and 45 7 15 6 9 and 3 7 wt nacl equivalent equiv respectively the majority of the inclusions within the handagai deposit have homogenization temperatures and salinities of 200 c 350 c and 4 14 wt nacl equiv respectively indicating that this is a medium high temperature and medium low salinity type deposit the fluid inclusions were trapped at pressures of 11 to 72 mpa corresponding to depths of 0 4 to 2 9 km the geology mineralogy geochemistry and fluid inclusions microthermometry indicate that the handagai deposit formed as a result of contact infiltration metasomatism with the deposition of ore minerals resulting from a combination of factors that include boiling as a result of reduced pressure cooling and fluid mixing

felsic magmatic phases and the role of late stage aplitic dykes in the formation of the world class cantung tungsten skarn deposit northwest territories canada abstract a field and petro chemical classification of felsic magmatic phases fmps at the world class cantung w skarn deposit was undertaken to document the evolution of magmatism and the relationships between different fmps metasomatism and mineralization early fmps include moderately differentiated zr hf 18 26 ti zr 14 15 biotite monzogranitic plutons and early biotite rich granitic dykes and compositionally similar quartz feldspar porphyry dykes late highly fractionated zr hf 8 17 ti zr 3 13 fmps sourced from a deeper monzogranitic intrusion include 1 leucocratic biotite or tourmaline bearing dykes derived from localized entrapments of residual magma and 2 sub vertical ne trending aplitic dykes derived from a larger segregation of residual fluid and incompatible element enriched magma the aplitic dykes have textures morphologies spatial associations and a pervasive calcic metasomatic mineral assemblage ca plagioclase quartz or clinozoisite indicative of syn mineralization emplacement very late stage overpressuring and initiation of sub vertical fractures into the overlying plutonic carapace and country rocks by supercritical magmatic fluid led to an interaction with calcareous country rocks that resulted in an increased aca2 in the fluid and the concurrent precipitation of w skarn residual magma also ascended with and quenched in equilibrium with the magmatic fluid to from the aplitic dykes then was metasomatized by the fluid as it interacted with calcareous country rocks overall highly fractionated and moderately to very highly undercooled fmps at cantung provide evidence for a large and evolving felsic magmatic system at depth that segregated and maintained a stable fluid and incompatible element enriched residual magma until the latest stages of crystallization the detailed study of fmps associated with magmatic hydrothermal mineral deposits allow us to refine our understanding of these mineralizing systems and better define metallogenic and exploration models for intrusion related mineralization

synthetic fluid inclusions xvii pvtx properties of high salinity h2o nacl solutions 30 wt nacl application to fluid inclusions that homogenize by halite disappearance from porphyry copper and other hydrothermal ore deposits fluid inclusions that homogenize by disappearance of the halite crystal after the vapor bubble has disappeared have been reported from a wide range of ore forming systems while this inclusion type is most commonly observed in porphyry copper and similar magmatichydrothermal ore deposits they have also been reported from iron oxide copper gold iocg mississippi valley type orogenic lode greenstone gold massive sulfide unconformity u and mantotype deposits as well as from non ore associated granitoids and oceanic crust the lack of experimental data to interpret microthermometric data from these inclusions combined with poor petrographic characterization of inclusion origin has led to a wide range of inferred pt trapping conditions for the inclusions the relationship between liquid vapor homogenization temperature thl v halite dissolution temperature tmhalite and pressure has been determined using synthetic h2o nacl fluid inclusions that homogenize by halite disappearance the experimental data cover the range thl v 150 to 500 c and tmhalite 275 to 550 c an empirical equation describing the relationship between pressure thl v and tmhalite has been developed to estimate formation pressures from microthermometric data and is valid from pressures along the liquid vapor halite curve to 300 mpa a detailed literature review reveals that the results of this study cannot be applied retroactively to estimate pressures of previously reported inclusions that homogenize by halite dissolution for several reasons first most workers have not collected and reported the data in a manner that allows one to determine if the inclusions have trapped a single homogeneous phase and have not leaked or changed volume following trapping thus it is not possible to determine if the inclusions show consistent microthermometric behavior within a group of coeval inclusions additionally many published studies provide only summaries of results from numerous samples or present the data graphically precluding application of our results to individual inclusions however based on our review it appears that much of the published data for inclusions that homogenize by halite dissolution represent inclusions that have either trapped a halite crystal along with the liquid or have reequilibrated by necking and or stretching results from this study have been used to estimate minimum formation pressures for inclusions from the ditrau alkaline massif transylvania romania the musoshi stratiform copper deposit zaire the bismark skarn deposit northern mexico the naica chimneymanto deposit mexico the questa porphyry molybdenum deposit new mexico and the bingham canyon porphyry cu mo deposit utah in each case pressures estimated using results from the present study are in good agreement with previous pressure estimates however in some cases estimated pressures both our estimates as well as those of other authors appear to be unreasonably high based on the geologic setting at the time of formation these results highlight the currently limited understanding concerning pressures depths of ore formation

dem analyses and morphotectonic interpretation the plio quaternary evolution of the eastern ligurian alps italy abstract the ligurian alps italy straddle a complex and ill defined tectonic transition that accommodates eurasia adria shortening driving concurrent growth of the western alps and northern apennines we focus on the plio quaternary landscape evolution of the eastern part of the ligurian alps with the goal of defining the active tectonics through an analysis of topography drainage networks and river long profiles the ligurian alps have a steep seaward facing escarpment with topographic features reminiscent of the geomorphic markers preserved on both actively uplifting coastlines and passive margins for example there are seaward facing benches that are thought to be uplifted marine terraces common to active margins but the drainage divide of the seaward escarpment shows clear evidence of recent northward migration into the po foreland a process consistent with escarpment retreat characteristic of passive or subsiding margins this study explores the active tectonics consistent with these diverse landscape evolution pathways our analysis reveals that rock type strongly throttles the development of topographic relief drainage networks and northward migration of the drainage divide however we also identify segments of the escarpment that indicate recent base level falls through an analysis of modeled channel steepness and comparison with mean hillslope gradient the base level falls are consistent with numerous barbed tributaries that are best explained as recent stream captures no significant correlation among the stream captures at the drainage divide suspected marine terraces at the coast ligurian sea bathymetry and active seismicity indicates that the escarpment is the footwall of a segmented normal fault this normal fault is embedded in a regionally subsiding margin where actively uplifting segments lead to a straightened pinned drainage divide whereas relatively inactive segments permit divide migration into the footwall block these results are broadly consistent with rock uplift increasing eastward toward genova across the long suspected alps apennine sestri voltaggio fault zone they highlight the respective roles of legacy structures rock type and localized rock uplift in constructing a landscape in an otherwise extending and subsiding crustal retrowedge of an active subduction plate boundary

fluvial geomorphology and paleohydrology in japan abstract an introduction to fluvial geomorphology and paleohydrology in japan is provided for researchers who are unfamiliar with these topics studies by japanese geomorphologists are reviewed including those published only in japanese language journals emphasis is placed upon the following aspects 1 abundant sediment yields from steep watersheds subjected to frequent heavy rains despite heavily vegetated conditions 2 extensive sedimentation in mountain piedmonts and coastal fluvial plains especially during the holocene 3 catastrophic hydro geomorphological events associated with earthquakes and volcanic eruptions and 4 the impacts of the increased heavy rainfall during the pleistocene holocene transition on the post glacial development of hillslopes and alluvial fans these geomorphological characteristics differ from those in continental regions such as europe and north america indicating that research on japanese fluvial systems can contribute a great deal to the understanding of the global variety of fluvial geomorphology recent work on paleohydrological reconstruction in japan is also reviewed

different proportion of mantle derived noble gases in the cu fe and fe skarn deposits he ar isotopic constraint in the edong district eastern china abstract cu and fe skarns are two economically important types of skarn deposit worldwide but the critical factors controlling the difference in metal associations remain enigmatic the edong ore district china presents an excellent opportunity to study the differences between cu fe and fe skarn deposits we have measured he ar isotopes trapped in fluid released by crushing pyrite and chalcopyrite from four well known cu fe and fe deposits in the edong district eastern china with the aim of constraining their different fluid source and then discussing the factors controlling their variations between cu fe and fe skarns he ar isotopic compositions are markedly different between the cu fe and fe skarn deposits in the edong district 3he 4he ratios in the cu fe deposits are 0 75 1 87 ra and 40ar 36ar ratios are 300 472 by contrast he ar isotopic compositions in minerals from the fe deposits have lower 3he 4he and 40ar 36ar ratios of 0 08 0 93 ra and 299 361 respectively these results suggest that noble gas of the cu fe and fe skarn deposits in the edong district formed by variable degrees of mixing between a magmatic fluid containing a mantle component and modified air saturated water masw importantly he ar isotope data provide compelling evidence that contrasting fluid sources were involved in the formation of the cu fe and fe deposits i e mineralizing fluids of the cu fe deposits could have a greater contribution from mantle component and little involvement of masw than those of the fe deposits in the edong district this conclusion is consistent with obvious differences in the nature of the intrusions related to mineralization as well as sulfur isotopic compositions of sulfides in the cu fe and fe deposits it is most likely that different proportion of mantle derived noble gases play an essential role in controlling differences between the cu fe and fe skarn deposits

a quantitative analysis for geomorphic indices of longitudinal river profile a case study of the choushui river central taiwan due to the plate movement is considerably slow the human history record is too short to register landscape change for such a long time scale however longitudinal river profile can display watershed landscape characteristics therefore this paper applies a quantitative analysis of geomorphic indices coupled with some mathematical models for the choushui river and its six tributaries including the gradient index and slope area relationship the abnormally high sl and sl k values indicated that a decreasing trend from lower to mid stream areas and south lishan fault was higher than north lishan fault on the upstream areas and the result of slope area relationship also indicated that the regression line of the upper and lower steam exhibit an obvious right shift nearby lishan fault could be explained by geodynamic models of active deformation in taiwan area this study also found that the abnormally high values of sl k were affected by river and fault intersecting to form a high angle or perpendicular and the abnormally low values of sl k were affected by river along with a fault or form a low angle but the channel of junda river along with lishan fault is opposite based on quantitative results of these geomorphology indices this study suggests that the important factor influencing landscape of the choushui river watershed is tectonic uplift

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

river terrace development by concurrent fluvial processes and climatic changes abstract along the usui river in central japan three well developed terrace levels are observed each terrace is subdivided into two segments a filltop terrace along the upper reach and a strath terrace along the lower one three valley fillings with coarse gravel beds in the upper reach correspond to the last three glacial ages the positions of these valleysfills migrated upstream from the older terrace to the younger one to clarify the response of fluvial systems to climatic change terrace sediments were interpreted from the viewpoint of paleohydraulics using the grain diameter of terrace sediments paleo tractive forces were evaluated based on the correlation between tractive force and grain diameter of the sediment on the present river bed the valley filling was caused by the diminution in tractive force related to the decrease in heavy rain produced by typhoons during the glacial ages during the interglacial ages the reverse responses occurred due to the increased incidence of typhoons from another aspect of the development of river landforms the decrease in the liver channel gradient during the interglacial ages caused the transportational and or depositional area of coarse gravels to migrate upstream in the subsequent glacial ages

ore forming fluids and isotopic h o c s pb characteristics of the fujiashan longjiaoshan skarn w cu mo deposit in the edong district of hubei province china abstract the fujiashan longjiaoshan deposit is located in the southern area of the edong district of the middle lower yangtze river metallogenic belt w cu mo orebodies are found in the contact zone between the granodiorite porphyry and carboniferous to triassic carbonate strata four stages of ore formation are identified 1 the prograde skarn stage 2 retrograde skarn stage 3 quartz sulfide stage further subdivided into the early 3a and later 3b and 4 carbonate stage in this study we applied fluid inclusion microthermometry laser raman spectroscopy and h o c s pb isotopic compositions to constrain hydrothermal processes and ore precipitation mechanisms of the fujiashan longjiaoshan deposit early stage 1 and 2 ore forming fluids belong to a high temperature above 550 c high salinity 60 70 wt nacl equiv and 15 20 wt nacl equiv respectively high pressure above 700 bars and high oxygen fugacity nacl kcl h2o system and in the quartz sulfide stage 3 the system changes into a nacl kcl co2 h2o system homogenization temperatures and salinities of ore forming fluids gradually decrease throughout the evolutionary process fluid temperatures vary at 550 c in prograde skarn stage 1 from 350 to 400 c in retrograde skarn stage 2 from 250 to 300 c in quartz sulfide stage 3 and finally from 100 to 150 c in carbonate stage 4 salinity levels vary from 15 to 20 wt nacl equiv in prograde skarn stage 1 from 5 to 20 wt nacl equiv in retrograde skarn stage 2 from 10 to 15 wt nacl equiv in quartz sulfide stage 3a from 5 to 10 wt nacl equiv in quartz sulfide stage 3b and from 0 to 5 wt nacl equiv in carbonate stage 4 the h o c isotopic compositions indicate that the ore forming fluids were derived from magmatic water d of 123 to 83 18ov smow of 6 1 to 7 4 with the input of meteoric water and organic matter in the quartz sulfide stage d of 91 to 53 18ov smow of 2 4 to 4 6 and cv pdb of 14 7 to 6 4 sulfur and pb isotopic compositions show that the ore forming materials were mainly derived from granitic magma 34sv cdt values of granodiorite porphyry sulfides and skarns of 5 7 to 6 6 and in part from host sedimentary strata 34sv cdt values of sulfides of country rocks clustering at 20 and at 10 fluid boiling in the retrograde skarn stage gave rise to the first precipitation of scheelite the precipitation of scheelite chalcopyrite and molybdenite in the quartz sulfide stage was probably triggered by the input of meteoric water and organic carbon according to mineral assemblages and all available geological and geochemical data we conclude that the fujiashan longjiaoshan deposit is an oxidized skarn type w cu mo deposit

evidence for late stage fluvial activity in kasei valles mars 1 two inner channels in the southern branch of kasei valles are among the best preserved examples of fluvial erosion on mars attributes of the channels include arcuate alcoves perched boulders and a concave up longitudinal profile all of which are consistent with the interpretation that these channels were carved by a newtonian fluid the sharp concavity of the longitudinal profile is comparable to a terrestrial alluvial system with a minimum work profile the shape of the profile suggests that the system was in a quasi equilibrium state but was not active long enough to achieve grade associated with these channels is a platy meter scale texture identified in high resolution mars orbiter camera images although a lava flow could explain many of the material properties of the platy surface texture we speculate that this texture in the immediate proximity to the southern kasei valles inner channels may be related to waning floodwaters moving through the inner channels and is a mudflow deposit

small profile concavity of a fine bed alluvial channel although most natural streams have concave upward longitudinal profiles there are conflicting perspectives about whether an alluvial channel is less concave than a bedrock channel alluvial channels can be classified as coarse bed and fine bed channels depending on the bed grain size both are transport limited but the threshold of motion differs greatly whereas a coarse bed alluvial channel can be claimed to be as concave as a bedrock channel we claim that a fine bed channel is distinguishably less concave we derive the concavity index of a fine bed alluvial channel using the power law relationships emergent at a steady state river network for known ranges of the scaling parameters our formulation informs a range of concavity index as 0 07 0 09 for a fine bed alluvial channel our analyses of previous laboratory experiments and real fine bed alluvial channels in the midwestern u s and northern europe also support our conclusions i e small profile concavity of steady state fine bed alluvial channels

profile convexities in bedrock and alluvial streams abstract longitudinal profiles of bedrock streams in central kentucky and of coastal plain streams in southeast texas were analyzed to determine the extent to which they exhibit smoothly concave profiles and to relate profile convexities to environmental controls none of the kentucky streams have smoothly concave profiles because all observed knickpoints are associated with vertical joints if they are migrating it either occurs rapidly between vertical joints or migrating knickpoints become stalled at structural features these streams have been adjusting to downcutting of the kentucky river for at least 1 3 ma suggesting that the time required to produce a concave profile is long compared to the typical timescale of environmental change a graded concave longitudinal profile is not a reasonable prediction or benchmark condition for these streams the characteristic profile forms of the kentucky river gorge area are contingent on a particular combination of lithology structure hydrologic regime and geomorphic history and therefore do not represent any general type of equilibrium state few stream profiles in se texas conform to the ideal of the smoothly strongly concave profile major convexities are caused by inherited topography geologic controls recent and contemporary geomorphic processes and anthropic effects both the legacy of quaternary environmental change and ongoing changes make it unlikely that consistent boundary conditions will exist for long further the few exceptions within the study area i e strongly and smoothly concave longitudinal profiles suggest that ample time has occurred for strongly concave profiles to develop and that such profiles do not necessarily represent any mutual adjustments between slope transport capacity and sediment supply the simplest explanation of any tendency toward concavity is related to basic constraints on channel steepness associated with geomechanical stability and minimum slopes necessary to convey flow this constrained gradient concept cgc can explain the general tendency toward concavity in channels of sufficient size with minimal lithological constraints and with sufficient time for adjustment unlike grade or equilibrium based theories the cgc results in interpretations of convex or low concavity profiles or reaches in terms of local environmental constraints and geomorphic histories rather than as disequilibrium features

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

the morphology of graded gravel rivers a network perspective analytical hydraulic geometry equations are combined with a watershed model to quantify downstrem trends in equilibrium fluvial morphology in gravel streams the hydraulic geometry equations relaet fluvial morphology to discharge bedload transport rate and grain size these independent variables are in turn determined by routing gravel supplied at zero order basins through a channel network as gravel is routed downstream it decreases in size according to an empirical power law the resulting model specifies the discharge bedload transport rate grain size width depth slope and river bed elevation at every point in the drainage basin when the downstream fining law is calibrated using data from central pennsylvania dowstream hydraulic geometry exponents for the width and depth are accurately reproduced longitudinal profiles calculated from the model fit observed profiles in largerwatersheds but are inaccurate in smaller watersheds the model also reproduces hack s 1957 empirical result relating slope to the 0 6 power of a ds where a is the drainage basin area and ds is the mean grain size unfortunately the model requires an equilibrium time scale which is unreasonably long suggesting that the channels of the study area are best described as systems with multiple time scales and multiple rates of response the model probably is successful because the width and depth have relatively short relaxation times and also because downstream trends in discharge and sediment transport rate are controlled by network topology thus downstream hydraulic geometry equations do not necessarily provide strong evidence for the equilibrium of fluvial landscapes rather they reflect the constancy of network topology and the rapid response times of width and depth

geology mineralization and fluid inclusion characteristics of the chorukh dairon w mo cu skarn deposit in the middle tien shan northern tajikistan abstract the chorukh dairon deposit is part of the metallogenic belt of w mo cu mo au w and au deposits along the late paleozoic active continental margin of the tien shan it is related to the late carboniferous multiphase pluton with successive intrusive phases of early monzogabbro through monzonite quartz monzonite to monzogranite and leucogranite and the latest lamprophyre dikes the deposit is an example of complex w mo cu magmatic hydrothermal system related to magnetite series shoshonitic igneous suite it contains zones of w cu mo oxidized prograde and retrograde skarns with abundant scapolite plagioclase k feldspar andradite garnet magnetite as well as molybdoscheelite and minor chalcopyrite and molybdenite skarns are overprinted by hydrosilicate alteration assemblages with amphibole chlorite epidote quartz calcite scapolite albite scheelite and chalcopyrite and are cut by quartz carbonate barite fluorite sulfide veins the fluid evolution included a release of high temperature 400 500 c high pressure 900 1100 to 700 800 bars high salinity magmatic hydrothermal aqueous chloride fluid with its direct separation from crystallizing magma and formation of prograde and retrograde skarns fluid enrichment in ca up to 15 22 wt cacl 2 at the retrograde skarn stage was possibly related to magmatic differentiation and provided intense molybdoscheelite deposition from a homogenous fluid in contrast hydrosilicate alteration assemblages were formed at lower temperatures 350 400 c initially from a homogenous and then from a boiling ca rich 20 22 wt cacl 2 magmatic hydrothermal fluid with the latter contributing to the most intense scheelite deposition the stable isotope data 13 c co 2 3 0 0 5 and 18 h 2 o 6 5 0 5 34 s 7 5 to 7 7 obtained for the hydrosilicate stage minerals suggest significant fluid sourcing from magmatic and meteoric waters as well as from sedimentary rocks enriched in seawater sulfate possibly evaporites although a strongly homogenous character of the isotopic composition reveals intense isotope homogenization in a magmatic chamber some light sulfur isotope enrichment of sulfides from the quartz carbonate barite fluorite sulfide veins 34 s 6 0 to 6 1 may be linked to the evolution of the magmatic source toward more mantle related sulfur species as these veins were formed after emplacement of the late mafic lamprophyre dikes

distribution of hazard types in a drainage basin and its relation to geomorphological setting abstract hazards along a river course in a drainage basin are characterized by three types of events debris flow turbidity flow and flood each has its own channel segment with different sediment transport processes the sediment transport process is controlled by transportation force tractive force and slope direction component of sediment weight both of which are significantly affected by channel slope along large rivers in japan the boundary between the upstream turbidity flow segment and the downstream flood segment is located at the position with a channel slope of about 1 1000 along steep small rivers the boundary between the upstream debris flow segment and the downstream turbidity flow segment is located at the position with a channel slope of about 80 1000 the channel slope depends on the shapes of longitudinal profiles of rivers the longitudinal profiles of japanese rivers main rivers and tributaries can be described by an exponential power or linear function the transportation force of the rivers fitted with exponential functions markedly decreases downstream due to the large curvature of the profiles causing noticeable sediment deposition in the middle courses the transportation force of the rivers fitted with power or linear functions maintains its strength through the whole river courses due to the small curvature causing sediment transportation down to the lower courses the function types are strongly affected by relief in the drainage basins the rivers flowing in small relief areas are fitted with exponential functions and those flowing in large relief areas are fitted with power or linear functions thus the distribution of hazard types along a river course in a drainage basin is controlled by the distribution of relief in the drainage basin

mineral chemistry and h o s pb isotopic compositions of skarn type copper deposits in the jiurui district of the middle lower yangtze river metallogenic belt eastern china abstract the skarn type copper deposits are widespread in the jiurui district in the middle lower yangtze river metallogenic belt this paper reports a detailed study on mineral chemistry and h o s and pb isotopic compositions on skarn silicate and sulfide minerals in the three major skarn dominant deposits wushan dongleiwan and dengjiashan the wushan skarn deposit is characterized with prograde garnet dominated and clinopyroxene limited skarns with average andradite content of 83 and hedenbergite content of 10 whereas the dongleiwan and dengjiashan deposits are featured with retrograde skarn alteration with abundant hydrous minerals such as epidote and chlorite the garnet and clinopyroxene compositions show 59 andradite and 15 hedenbergite for the dongleiwan skarns and 43 and 22 for the dengjiashan skarns respectively the pistacite components ps value defined as fe3 fe3 al and fe3 fe2 value of epidote are 0 12 and 1 63 for the wushan skarns 0 30 and 32 73 for the dongleiwan skarns and 0 17 and 42 85 for the dengjiashan skarns it is suggested that the prograde skarn mineralization in the three deposits was all formed in a relatively oxidizing environment with the wushan showing the highest oxidation potential and the dengjiashan having the least oxidation potential however in the retrograde skarns the dongleiwan and dengjiashan deposits show higher oxidation potential than that of wushan the three deposits show similar sulfur isotopic compositions of 2 9 to 1 4 and similar lead isotopic compositions with 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 900 to 18 205 15 538 to 15 649 and 38 170 to 39 025 respectively all the three deposits should have similar magmatic origin for the ore forming materials based on their s and pb isotopes the oxygen isotopic compositions of the prograde and retrograde fluids in the three deposits show some differences with 18ofluid values of 8 13 and 7 81 for the wushan 6 47 and 2 33 for the dongleiwan and 8 27 and 4 43 for the dengjiashan but the hydrogen isotopic compositions are similar for the prograde 65 to 31 and retrograde 64 to 33 fluids therefore the fluid origins and evolution may be different in each deposit the hydrothermal fluids for the prograde skarns in all three deposits were likely derived from magmatic hydrothermal sources but the dongleiwan and dengjiashan show a higher proportion of meteoric water input in the retrograde stage considering the similar average prograde temperatures 574 to 560 c as calculated from coexisting garnet clinopyroxene pairs and similar retrograde temperatures 281 to 246 c as calculated from chlorite chemistry for the three deposits we suggest that the trigger for deposition of sulfide ores in the wushan garnet dominated skarn deposit was mainly caused by system cooling with temperature drop along with magmatic intrusion and crystallization process the dongleiwan and dengjiashan skarn deposits constitute a well developed retrograde skarn system with abundant epidote chlorite quartz and calcite which probably caused by fluid mixing of high temperature saline magmatic hydrothermal fluids with cooler oxidizing and dilute meteoric water

fluid inclusions in skarns carbonate replacement deposits fluid inclusions in ore skarn minerals reflect the physiochemical nature of the solutions present during the skarn forming process because of the dense nature of skarn minerals and the dynamic processes operative during skarn genesis sufficient primary fluid inclusions are usually present ore skarn solutions as opposed to metamorphic skarn or ore vein solutions have much higher cacl2 contents and usually very high formation temperatures 500 c and salinities 40 wt t d s temperatures and salinities generally decrease away from the solution source both in time and space the gradients found at greater distances from the source in distal far from contact skarns tend to be less e g 210 350 c for a particular skarn stage to that in proximal near contact skarns e g 400 650 c this information is useful for delineating the parts of such a hydrothermal system temperatures also tend to decrease with time which is reflected by the superimposition of various overprinting retrograde mineral stages in a few areas e g naica mexico intermittent boiling of ore solutions occurs periodically elevating both temperatures and salinities but commonly boiling only occurs early in skarn genesis just after an early commonly lower temperature phase most fluid inclusions represent a mix of exhaust or reacted solutions with minor unreacted or new pre ore solution components limited data on the distribution of elements present in fluid inclusions that do not normally take part in skarn genesis na k and cl indicate that their proportions reflect the nature of the associated pluton high kc1 contents are found in skarns adjacent to high k granitoids whereas high nacl contents are found in skarns adjacent to calcic granitoids in many examples daughter minerals present in minor proportions in opened fluid inclusion cavities reflect the metal characteristics of the ore solution small rare earth metal tungsten zinc and copper daughter minerals have been identified the temperature and or salinity data for skarns of different metal or geological type is not particularly useful to delineate whether a skarn locality is part of a more complex as yet unexplored system solutions in pb zn skarns tend to be lower temperature 150 400 c and more dilute 30 wt t d s than in other skarn types but exceptions occur

headwater peatland channels in south eastern australia the attainment of equilibrium abstract many small headwater catchments 2 in temperate south eastern australia store sediment in valley fills while accumulation in some of these systems commenced up to 30 000 years ago most did not commence filling with peat or clastic material until at least the mid holocene in such headwater settings many clastic valley fills develop cut and fill channels which contrast to some peatland settings where sinuous equilibrium channels have evolved four peatland systems within this dataset demonstrate stable channel systems which span nearly the full spectrum of observed valley floor slopes we assess new and published longitudinal data from these four channels and demonstrate that each of these channels has achieved equilibrium profiles new and published flow and survey data are synthesised to demonstrate how these peatland systems have attained equilibrium low rates of sediment supply and exceptionally high bank strengths have resulted in low width to depth ratios which accommodate rapid changes in flow velocity and depth with changes in discharge in small peatland channels planform adjustments have been sufficient to counter the energy provided by these hydraulically efficient cross sections and have enabled the achievement of regime energy slopes in larger and higher energy peatland channels large armoured stable bedforms have developed these bedforms integrate with planform adjustments to maintain a condition of minimum variance in energy losses as represented by the slope profiles and therefore a uniform increase in downstream entropy

downstream fining in a network of gravel bedded rivers a network based routing model is used to determine how spatial variations in sediment supply influence rates of downstream fining in a small watershed in central pennsylvania gravel of a specified size distribution and lithology is supplied to the network at zero order basins once in transport the total sample weight and moments of the grain size distribution are modified according to empirical functions of transport distance contributions from each zero order basin are summed to determine the total population of sizes and lithologies at any location in the study area resistant quartz sandstone ridges supply sediment an order of magnitude larger than other lithologies because these ridges occur primarily in the basin headwaters spatial variations in supply strongly influence rates of downstream fining model calculations indicate that spatial variations in supply alone account for over 80 of the decrease in mean grain size along the main channel

geomorphological evolution of longitudinal river profiles in the carpathians abstract the main rivers which drain the east and southeast side of the eastern carpathians and those that drain the southern carpathians have been analysed regarding the sediment transit the change of the riverbeds and the type of channel deposits in this paper attention is focused on the concavity of the stream profile on this basis we tried to determine the evolution of some carpathian rivers and thus estimate their long term evolutionary tendencies the concavity index of the east carpathian rivers shows a trend to increase from north to south from the eastern carpathians to the carpathian bend and the bucegi mountains the explanation of this situation required a review of the evolutionary stages of the eastern carpathians in order to establish the age and the evolutionary tendencies of the river network in our study area the rivers suceava moldova and bistri a have followed the same courses since the sarmathian approximately 13 5 million years ago the trotus river between 10 million and 5 4 million years ago the rivers putna buz u prahova and ialomi a suffered the most important changes so the age of their present course is about 2 5 million years the rivers could be grouped according to the mathematical model which fits best the exponential exponential logarithmic and logarithmic model finally we tried to correlate the age of the river with the form of its longitudinal profile the customary theoretical models require that the older a river is the more its concavity should increase in the headwater area and should asymptotically approach a longitudinal equilibrium profile or grade as davis calls it however the carpathian rivers do not follow this general tendency what we have demonstrated is that age had no influence on the form of the longitudinal profiles for the rivers on the exterior side of the carpathians this is because tectonic uplift was important and this phenomenon is still present today with values of over 6 mm year

the role of sediment in controlling steady state bedrock channel slope implications of the saltation abrasion incision model abstract the saltation abrasion model is a mechanistic model for river incision into bedrock by saltating bedload which we have previously derived and used experimental data to constrain all parameter values here we develop a method for applying the saltation abrasion model at a landscape scale and use the model as a reference for evaluating the behavior of a wide range of alternative incision models in order to consider the implications of the saltation abrasion model as well as other models for predicting topographic steady state channel slope to determine the single valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock we assume all runoff can be partitioned between a low flow and a high flow discharge in which all bedload sediment transport occurs during high flow we then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for using the predictions of the saltation abrasion model as a reference we find that the threshold of motion is the most important effect that should be represented explicitly followed in order of decreasing importance by the cover effect the tools effect and the threshold of suspension effect models that lack the threshold of motion over predict incision rate for low shear stresses and under predict the steady state channel slope for low to moderate rock uplift rates and rock strengths models that lack the cover effect over predict incision rate for high sediment supply rates and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage models that lack the tools effect over predict incision rate for low sediment supply rates and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value overall the saltation abrasion model predicts that steady state channel slope is most sensitive to changes in grain size such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible but as yet poorly understood influence on the size distribution of sediments delivered to channel networks by hillslopes

modelling holocene stratigraphy and depocentre migration of the volga delta due to caspian sea level change the volga system is sensitive to allogenic control due to its low on and offshore gradient similar to 5 cm km in sequence stratigraphy little attention has been paid to the effects of sea level change in these ramp margin fluvio deltaic settings the high frequency sea level changes of the caspian basin have considerable amplitude up to 18 m over the holocene time span which is usually considered as the lower boundary of fifth order cycles a process response model aquatellus has been used to investigate fluvio deltaic response to sea level fluctuation calibration of the model with measured data over the last century comprising a full 3 m sea level cycle showed plausible progradation and sedimentation rates the numerical modelling showed that sea level changes forced the holocene volga delta to migrate similar to 200 km over the caspian plain leaving only thin laterally extensive deposits the frequent depocentre shifts add a whole new perspective to the ongoing discussion about the impact of sea level changes along the longitudinal profile the periods during which significant deposition occurred coincide with the times that migration distances were relatively low thicker progradational wedges have been deposited at these time intervals at similar to 9000 8000 similar to 7400 6700 similar to 5200 3700 and similar to 2400 900 years bp c 14 dated deposits in the lower delta plain area corroborate the model output remarkably this is both in highstand and lowstand conditions the low gradient makes wave effects insignificant and tides are nonexistent so that the fluvial deposits are hardly reworked and no shoreface facies or maximum flooding surface develop the volga delta response indicates that sequence stratigraphic concepts are not scale independent in low gradient settings and that short term high frequency sea level changes have a far reaching impact on the stratigraphy c 2002 elsevier science b v all rights reserved

tectonic uplift of the northern qinling mountains central china during the late cenozoic evidence from dem based geomorphological analysis abstract the qinling mountains which stretch from east to west in central china represent an important geological and geographical boundary between north china and south china because of the northeastward growth of the tibetan plateau since the late cenozoic the northern qinling mountains have been strongly reactivated and uplifted to investigate the landscape response to the tectonic uplift the geomorphic indices of the northern qinling mountains including the hypsometry mathematical function of the longitudinal profile channel longitudinal profile and steepness index were analyzed the topographic analysis reveals that the landscape evolution of the heihe river basin is in a transient state the upstream of the heihe river basin has undergone a long period of erosion and represents relict landscape in contrast the downstream represents adjusting landscape which formed by river incision in response to the rapid uplift of the northern qinling mountains this is a result of the extension of the weihe graben which has formed due to the northeastward growth of the tibetan plateau during the late cenozoic the spatial distribution of the geomorphic indices reveals that the ne striking taibai fault has experienced strong tectonic activity since the late cenozoic and is a secondary fault that accelerated the uplift rate of the northern qinling mountains the tectonic stress due to the northeastward growth of the tibetan plateau has been transmitted to the northern qinling mountains along the taibai fault therefore we proposed that the uplift of the northern qinling mountains is due to the combined effects of the weihe graben extension and taibai fault activity forming the highest peak taibai mountain of the northern qinling mountains near the intersection of the qinling piedmont fault and taibai fault

reconciling fluid inclusion types fluid processes and fluid sources in skarns an example from the bismark deposit mexico the bismark deposit 8 5 mt at 8 zn 0 5 pb 0 2 cu and 50 g t ag located in northern mexico is an example of a stock contact skarn end member of a continuum of deposit types collectively called high temperature carbonate replacement deposits the deposit is hosted by massive sulfide within altered limestone adjacent to the bismark quartz monzonite stock 42 ma and the bismark fault alteration concurrently developed in both the intrusion and limestone the former contains early potassic alteration comprising k feldspar and biotite which was overprinted by kaolinite rich veins and alteration and later quartz sericite and pyrite with minor sphalerite and chalcopyrite prograde exoskarn alteration in the limestone consists of green andradite and diopside and transitional skarn comprising red brown andradite green hedenbergite and minor vesuvinite calcite fluorite and quartz the main ore stage post dates calc silicate minerals and comprises sphalerite and galena with gangue pyrite pyrrhotite calcite fluorite and quartz the entire hydrothermal system developed synchronously with faulting fluid inclusion studies reveal several distinct temporal compositional and thermal populations in pre syn and post ore quartz fluorite and calcite the earliest primary fluid inclusions are coexisting vapor rich type 2a and halite bearing type 3a type 3b contain sylvite brine inclusions 32 to 60 total wt salts that occur in pre ore fluorite trapping temperatures are estimated to have been in excess of 400 c under lithostatic pressures of 450 bar 1 5 km depth primary fluid inclusions trapped in syn ore quartz display critical to near critical behavior type 1c have moderate salinity 8 4 to 10 9 wt nacl equiv and homogenization temperatures th ranging from 351 to 438 c liquid rich type 1a and 1b calcite bearing inclusions occur as primary to secondary inclusions predominantly in fluorite and show a range in th 104 336 c and salinity 2 7 11 8 wt nacl equiv which at the higher th and salinity ranges overlap with type 1c inclusions oxygen isotope analysis was carried out on garnet quartz and calcite plus carbon isotopes in pre syn post ore and peripheral veins pre ore skarn related garnets have a 18omineral range between 3 9 and 8 4 quartz from the main ore stage range between 13 6 and 16 0 calcite from the main ore stage has 13c values of 2 9 to 5 1 and 18o values of 12 3 to 14 1 which are clearly distinct from post ore veins and peripheral prospects that have much higher 18o 16 6 27 3 and 13c 1 3 3 1 values despite the numerous fluid inclusion types only two fluid sources can be inferred namely a magmatic fluid and an external fluid that equilibrated with limestone furthermore isotopic data does not indicate any significant mixing between the two fluids although fluid inclusion data may be interpreted otherwise thus the various fluid types were likely to have formed from varying pressure temperature conditions through faulting during exsolution of magmatic fluids late stage hydrothermal fluid activity was dominated by the non magmatic fluids and was post ore

a petrological and fluid inclusion study of magnetite scheelite skarn mineralization at kara northwestern tasmania implications for ore genesis abstract the kara magnetite scheelite deposit is located about 40 km south of burnie in northwestern tasmania the deposit consists of a number of orebodies and the total mineable reserves are 1 7 mt of magnetite at 30 fe and 0 3 mt of scheelite at 0 52 wo3 the major orebodies at kara are hosted by the ordovician gordon limestone at the southern end of the devonian housetop granite adjacent to the granite or separated from it by the ordovician moina sandstone at least four paragenetic stages of skarn formation and ore deposition have been recognized stage i clinopyroxene garnet vesuvianite wollastonite quartz scheelite stage ii garnet vesuvianite magnetite scheelite apatite quartz stage iii magnetite amphibole epidote fluorite quartz chlorite garnet vesuvianite scheelite carbonate pyrite clinopyroxene and stage iv hematite fluorite calcite quartz fluid inclusions in clinopyroxene from stage i homogenize at 460 620 c mode 520 c stage ii gave homogenization temperatures of 349 578 c mode 500 c from scheelite and 360 570 c mode 500 c from vesuvianite the stage i clinopyroxene gave a salinity range of 10 0 12 0 equiv wt nacl with only one low value of 2 0 equiv wt nacl the stage ii mineral assemblages also showed moderate salinities of 12 0 and 17 8 equiv wt nacl from scheelite and vesuvianite fluid inclusions in quartz scheelite calcite and fluorite from the main scheelite mineralization phase stage iii homogenize at 230 360 c with a mode at 300 c and salinity varies from 0 2 to 19 8 equiv wt nacl the mineral paragenetic and fluid inclusion studies indicate that magnetite scheelite mineralization at kara was formed as a proximal skarn assemblage in carbonate host the skarn formation and ore deposition occurred in stages starting with prograde anhydrous clinopyroxene garnet metasomatism at relatively high temperatures 500 c this early assemblage was replaced by the subsequent retrograde deposition of hydrous mineral phases e g amphibole epidote and chlorite as temperatures decreased to 300 c or less deposition of scheelite predominantly occurred in association with hydrous minerals e g amphibole in stage iii the high temperature and moderate to high salinity ore fluids in early anhydrous skarn formation stages i and ii are consistent with fluids of magmatic origin in comparison the lower temperature and variable salinity from high 19 8 equiv wt nacl to as low as 0 2 equiv wt nacl in stage iii suggests a possible involvement of low salinity meteoric waters mixing with high salinity fluids originating from the nearby granite in the later hydrous skarn and ore formation

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

changes in the hypsometric curve through mountain building resulting from concurrent tectonics and denudation abstract the stages of geomorphic development of mountains have sometimes been explained based on strahler s diagram of hypsometric curves although the japanese mountains are young they do not follow his diagram hypsometric curves simulated using empirical laws deduced from the japanese mountains indicate that mountain building resulting from concurrent tectonics and denudation does not produce convex curves but concave and or s shaped curves the hypsometric curve of a mountain changes from a concave curve to an s shaped curve in accordance with the increase in mountain altitude the succession of the hypsometric curve during concurrent tectonics and denudation is the reverse of strahler s diagram the hypsometric integral increases with the advance in stage which is evaluated based on the change in mountain altitude it has a relatively good correlation with the stage however the sequence of change in the hypsometric integral is different according to the extent of the terrain examined whether the terrain is restricted to the interior of a mountain or pertains to the whole mountain and whether it includes newly emerged land the stage should be evaluated based on the course of change in the integral characteristics for the extent of the mountain examined

effects of tectonics and lithology on long profiles of 16 rivers of the southern central massif border between the aude and the orb france abstract the analysis of longitudinal profiles of river channels and terraces in the southern central massif border between the aude and the orb allows the detection of anomalies caused by lithology and or tectonic distortions the rivers which have abnormally high slope and non lithological knickzones indicate the main uplifted zones the montagne noire and the saint chinian ridge a geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations reconstructing the palaeodrainage and finding the main uplift and fluvial incision stages during the miocene uplift remains limited as it is shown by the correlative fine deposits in the languedocian piedmont the messinian incision 5 7 5 3 ma does not cross the saint chinian ridge on the other hand fluvial incision becomes widespread in the montagne noire during the upper pliocene 3 4 2 ma when coarse deposits overlie either the pliocene clay in the orb palaeovalley or the messinian conglomerates at the cesse outlet an upper pliocene uplift of the montagne noire and of the saint chinian ridge is the cause of this incision and also of the diversion of the cesse towards the aude where the uplift rate was higher than incision rate knickzones have developed like in the avant monts south side the knickzones of lithological origin maintain a strong vertical stability during all the river incision stages on the other hand those of tectonic origin or base level lowering record upstream migration and their rate of retreat is controlled by the river discharge as incision occurs only during the cold temperate transition periods during the quaternary upward erosion slowly migrates 15 km since the upper pliocene on the orb and so does not reach the riverheads

in situ la icpms trace elements and u pb analysis of titanite from the mesozoic ruanjiawan w cu mo skarn deposit daye district china abstract in this paper we present u pb ages and trace element compositions of titanite from the ruanjiawan w cu mo skarn deposit in the daye district eastern china to constrain the magmatic and hydrothermal history in this deposit and provide a better understanding of the u pb geochronology and trace element geochemistry of titanite that have been subjected to post crystallization hydrothermal alteration titanite from the mineralized skarn the ore related quartz diorite stock and a diabase dike intruding this stock were analyzed using laser ablation inductively coupled plasma mass spectrometry la icpms titanite grains from the quartz diorite and diabase dike typically coexist with hydrothermal minerals such as epidote sericite chlorite pyrite and calcite and display irregular or patchy zoning these grains have low lree hree and high th u and lu hf ratios coupled with negative eu and positive ce anomalies the textural and compositional data indicate that titanite from the quartz diorite has been overprinted by hydrothermal fluids after being crystallized from magmas titanite grains from the mineralized skarn are texturally equilibrated with retrograde skarn minerals including actinolite quartz calcite and epidote demonstrating that these grains were formed directly from hydrothermal fluids responsible for the mineralization compared to the varieties from the quartz diorite stock and diabase dike titanite grains from the mineralized skarn have much lower ree contents and lree hree th u and lu hf ratios they have a weighted mean 206 pb 238 u age of 142 2 ma mswd 0 7 2 in agreement with a zircon u pb age of 144 1 ma mswd 0 3 2 of the quartz diorite and thus interpreted as formation age of the ruanjiawan w cu mo deposit titanite grains from the ore related quartz diorite have a concordant u pb age of 132 2 ma mswd 0 5 2 which is 10 12 ma younger than the zircon u pb age of the same sample and thus interpreted as the time of a hydrothermal overprint after their crystallization this hydrothermal overprint was most likely related to the emplacement of the diabase dike that has a zircon u pb age of 133 1 ma and a titanite u pb age of 131 2 ma the geochronological results thus reveal two hydrothermal events in the ruanjiawan deposit an early one forming the wu cu mo ores related to the emplacement of the quartz diorite stock and a later one causing alteration of the quartz diorite and its titanite due to emplacement of diabase dike it is suggested that titanite is much more susceptible to hydrothermal alteration than zircon results from this study also highlight the utilization of trace element compositions in discriminating titanite of magmatic and hydrothermal origins facilitating a more reasonable interpretation of the titanite u pb ages

origin and interpretation of knickpoints in the big south fork river basin kentucky tennessee this study investigates the causes of knickpoints and knickzones in the bedrock controlled streams of the big south fork river basin in kentucky and tennessee knickpoints in the big south fork river area vary in form and apparent origins while some are likely related to base level change and incision in the cumberland river drainage system the locations and drainage relations of the knickpoints are not consistent with transmission of an incision signal throughout the network local controls predominate in forming steeper channel segments with no single factor dominant knickpoints in the study area are characterized by polygenesis and multiple causality though several archetypes can be identified these include rock fall rapids created by mass wasting from adjacent valley slopes structurally controlled headwater cliffs and lithological knickpoints a fourth category local incision knickpoints may be attributable to a variety of factors influencing force resistance relationships these results imply that the simple presence of a knickpoint cannot be attributed to any particular cause or history without consideration of the local controls this further implies that factors such as the spacing of knickpoints may not be an indication of migration rates or that migration has even occurred however the analysis of individual profile convexities can shed light on various controls such as lithology and structure and other processes such as valley side mass wasting and local bed incision important in evolution of fluvially dissected landscapes

geology mineralization and fluid inclusion characteristics of the lermontovskoe reduced type tungsten cu au bi skarn deposit sikhote alin russia abstract the lermontovskoe deposit 48 kt wo 3 average 2 6 wo 3 0 24 cu 0 23 g t au is situated in a w sn au metallogenic belt that formed in a collisional tectonic environment this tungsten skarn deposit has a w au as bi te sb signature that suggests an affinity with reduced intrusion related au deposits the deposit is associated with an intrusion that is part of the ilmenite series high k peraluminous granitoid granodiorite to granite suite these rocks formed via mantle magma induced melting of crustal sources the deposit comprises reduced type pyroxene dominated prograde and retrograde skarns followed by hydrosilicate amphibole chlorite pyrrhotite scheelite quartz and phyllic muscovite sericite carbonate albite quartz scheelite sulfide with abundant apatite alteration assemblages fluid inclusions from the skarn assemblages indicate high temperature 500 c high pressure 1400 1500 bars and high salinity 53 60 wt nacl equiv magmatic hydrothermal fluids they were post dated by high carbonic methane dominate low salinity fluid at the hydrosilicate alteration stage these fluids boiled at 360 380 c and 1300 1400 bars the subsequent phyllic alteration started again with a high temperature 450 c high pressure 1000 1100 bars and high salinity 42 47 wt nacl equiv fluid with further incursion of high carbonic methane dominated low salinity fluid that boiled at 390 420 c and 1150 1200 bars the latest phyllic alteration included the lower temperature 340 360 c lower pressure 370 400 bars high carbonic methane dominated but with higher co 2 fraction low salinity fluid and then the low temperature 250 300 c h 2 o co 2 ch 4 nacl fluid with both fluids boiled at the deposit level the high salinity aqueous fluids are interpreted to have come from crystallizing granitoid magma whereas the reduced high carbonic fluids probably came from a deeper mafic magma source both of these fluids potentially contributed to the w au as bi te sb metal budget decreasing temperatures coupled with high aca 2 and fluid boiling promoted scheelite deposition at all post skarn hydrothermal stages the deposit is characterized by limited downdip extent of mineralized zones and abundant coarse grained muscovite quartz apatite scheelite aggregates that formed at the phyllic alteration stage together with presence of high temperature high pressure and high salinity fluids directly exsolving from crystallizing magma this suggests a root level of the mineralized magmatic hydrothermal system of reduced w skarn deposits

longitudinal profiles in simple alluvial systems theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading alluvial systems that are unaffected by significant lateral inputs of water or sediment a new set of field data confirms this for individual sedimentary links along a wandering gravel bed river in british columbia canada each link is viewed as a simple alluvial system without major water or sediment inputs within which grain size typically fines downstream in a relatively systematic manner such homogeneous reaches are suitable for the investigation of simple profile form it is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles overall the river forms an irregularly cuspate long profile structured by these fundamental length scale units both link gradients and link fining rate reflect size selective aggradation associated with the bounding lateral inputs

quantifying the transient landscape response to active faulting using fluvial geomorphic analysis in the qianhe graben on the southwest margin of ordos china abstract river morphology has been widely used to record and track the transient landscape response to active faulting here we evaluate the landscape response to active faulting in the qianhe graben of southwest ordos china in this region it has been difficult to determine the activity of mapped faults because of the presence of thick quaternary loess however by analysing the presence and distribution of slope break knickpoints in river longitudinal profiles the ongoing tectonic uplift of the qianhe graben can be investigated the alignment of vertical step knickpoints gives a new insight into the location of an active fault on the southern margin of qianhe graben additionally slope break knickpoints typical of fault controlled landscape change were identified from 24 river longitudinal profiles that drain across normal faults along both graben margins along strike from north to south the knickpoints varied systematically with relief and the height of the knickpoints also decrease to the southeast indicating that the rate of motion on the faults likely is greater in the northwest and decays southeastwards the horizontal knickpoint retreat rates range from 0 3 to 27 3 mm yr constraining the landscape response time with fault initiation at 1 2 1 4 myr in comparison with other studies the knickpoint recession triggered by base level fall as a result of faulting is relatively lower than when the base level fall is the result of sea level fall potentially the result of different mechanism of retreat finally the potential for earthquakes along the taoyuan guichuansi fault tgf before and after fault linkage was assessed indicating the potential for earthquakes of mw of 6 3 6 7 and 6 8 7 0 respectively these observations not only suggest the knickpoints are recording fault evolution in qianhe graben but also provide information on seismic hazard in this populous region

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

geochemical constraints on cu fe and fe skarn deposits in the edong district middle lower yangtze river metallogenic belt china abstract copper and iron skarn deposits are economically important types of skarn deposits throughout the world especially in china but the differences between cu and fe skarn deposits are poorly constrained the edong ore district in southeastern hubei province middle lower yangtze river metallogenic belt china contains numerous fe and cu fe skarn deposits in this contribution variations in skarn mineralogy mineralization related intrusions and sulfur isotope values between these cu fe and fe skarn deposits are discussed the garnets and pyroxenes of the cu fe and fe skarn deposits in the edong ore district share similar compositions i e dominantly andradite ad 29 100 gr 0 68 and diopside di 54 100 hd 0 38 respectively this feature indicates that the mineral compositions of skarn silicate mineral assemblages were not the critical controlling factors for variations between the cu fe and fe skarn deposits intrusions associated with skarn fe deposits in the edong ore district differ from those cu fe skarn deposits in petrology geochemistry and sr nd isotope intrusions associated with fe deposits have large variations in their la yb n ratios 3 84 24 6 and eu anomalies eu 0 32 1 65 and have relatively low sr y ratios 4 2 44 0 and high yb contents 1 20 11 8 ppm as well as radiogenic sr nd isotopes end t 12 5 to 9 2 and 87 sr 86 sr i 0 7067 to 0 7086 in contrast intrusions associated with cu fe deposits are characterized by relatively high sr y 35 0 81 3 and la yb n 15 0 31 6 ratios low yb contents 1 00 1 62 ppm without obvious eu anomalies eu 0 67 0 97 as well as 87 sr 86 sr i 0 7055 to 0 7068 and end t 7 9 to 3 4 geochemical evidence indicates a greater contribution from the crust in intrusions associated with fe skarn deposits than in intrusions associated with cu fe skarn deposits in the edong ore district the sulfides and sulfates in the cu fe skarn deposits have sulfur isotope signatures that differ from those of fe skarn deposits the cu fe skarn deposits have a narrow range of 34 s values from 6 2 to 8 7 in sulfides and 13 2 to 15 2 in anhydrite while the fe skarn deposits have a wide range of 34 s values from 10 3 to 20 0 in pyrite and 18 9 to 30 8 in anhydrite sulfur isotope data for anhydrite and sedimentary country rocks suggest that the formation of skarns in the edong district involved the interaction between magmatic fluids and variable amounts of evaporites in host rocks

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

slope of alluvial fans in humid regions of japan taiwan and the philippines abstract this study constructed a database for 690 alluvial fans in humid regions of japan taiwan and the philippines and analyzed their slopes and other morphometric parameters such as the area and relief ratio of the source area this type of comprehensive geomorphological research on alluvial fans in humid regions has been limited although numerous studies have dealt with fans in arid and semi arid regions semi conical depositional landforms larger than 2 km2 and steeper than 0 11 0 002 m m were selected as alluvial fans about 60 of the fans formed during the holocene and the rest 40 formed during the pleistocene mean fan slopes for both all the quaternary fans and holocene fans follow a lognormal frequency distribution the distribution also fits slopes of fans belonging to a certain areal range the area and relief ratio of the source area which correlate well with the fan slope also follow a lognormal distribution indicating the dimensions of fan basin systems vary gradually rather than abruptly these findings contrast with a previous notion that depositional landforms rarely have slopes of 0 5 0 009 to 1 5 0 026 and hence only semi conical landforms steeper than 1 5 should be called alluvial fans

a worldwide correlation for exponential bed particle size variation in subaerial aqueous flows the particle size of the bed sediments in or on many natural streams alluvial fans laboratory flumes irrigation canals and mine waste deltas varies exponentially with distance along the stream a plot of the available worldwide exponential bed particle size diminution coefficient data against stream length is presented which shows that all the data lie within a single narrow band extending over virtually the whole range of stream lengths and bed sediment particle sizes found on earth this correlation applies to both natural and artificial flows with both sand and gravel beds irrespective of either the solids concentration or whether normal or reverse sorting occurs this strongly suggests that there are common mechanisms underlying the exponential diminution of bed particles in subaerial aqueous flows of all kinds thus existing models of sorting and abrasion applicable to some such flows may be applicable to others a comparison of exponential laboratory abrasion and field diminution coefficients suggests that abrasion is unlikely to be significant in gravel and sand bed streams shorter than about 10 km to 100 km and about 500 km respectively copyright c 1999 john wiley sons ltd

emergence and pseudo equilibrium in geomorphology abstract many geomorphic system states and behaviors often interpreted as tendencies toward establishment and maintenance of steady state equilibrium are actually emergent outcomes of two simple principles gradient selection and threshold mediated modulation the principle of gradient selection is simply that geomorphic features associated with gradient driven flows persist and grow relative to other features and pathways the principle of threshold mediated modulation reflects the inherent limits on system development along any particular pathway thresholds not only define a restricted state space for any given geomorphic system but may also result in oscillatory behavior around an intermediate condition that resembles fluctuations around a steady state equilibrium together these principles often produce outcomes that mimic steady state equilibria examples are given involving several aspects of fluvial systems channel profiles alluvial channel changes and drainage density hillslope gradients and barchan dunes steady states indeed occur in earth surface systems and are a useful simplification in some models however the assumption that such states are somehow normative or the only natural condition is incorrect and can lead to problems in geomorphic interpretations environmental restoration and management and conceptions of how earth systems work

longevity of magmatic hydrothermal systems in the daye cu fe au district eastern china with implications for mineral exploration the daye district represents one of the largest concentrations of cu fe au skarn deposits in china with additional porphyry cu mo deposits these deposits are closely associated with late mesozoic intrusions of intermediate to felsic composition previous studies have yielded important age constraints for several deposits timing and history of metallogenesis for the entire district however remain not well understood in this paper we present twenty five new ages re os 40ar 39ar and u pb to better understand the temporal framework of the district wide polymetallic mineralization these ages when combined with existing data indicate a prolonged history of mineralization lasting 25 million years from late jurassic to early cretaceous 157 132 ma and that most ore deposits of the district are results of multistage hydrothermal activity discrete episodes of ore formation coincide well with emplacement ages of granitoid intrusions within the district as revealed by recent zircon u pb dating this age consistency substantiates a genetic relationship between ore formation and intrusive magmatism prolonged and episodic magmatic and hydrothermal activities must have played significant roles in the formation of polymetallic ore deposits in the district by repeatedly supplying heat fluids and metals previous studies have demonstrated that the daye district was dominated by lithospheric extension during late jurassic to early cretaceous when extensive magmatism and mineralization took place under the extensional setting the area could have experienced significant uplift or extensional exhumation that would have brought early stage intrusions and associated ore deposits to shallower levels with ore bodies formed by subsequent magmatic hydrothermal events tending to be localized at greater depth this in turn indicates potentials to find new ore bodies at depth of known deposits especially for those formed by episodic magmatic hydrothermal processes this view is partly confirmed by the recent success in deep exploration beneath the tieshan fe cu and tonglushan cu au fe deposits

development of longitudinal profiles of alluvial channels in response to base level lowering degradation of alluvial channels in cohesive sediments was studied in 15 m and 20 m long flumes with a slope of 0 01 cm cm degradation was initiated by lowering base level to a fixed position and the development of the longitudinal profile of the channel is analysed through a model formulated as a heat diffusion equation it is based on the equation of sediment continuity combined with an assumption regarding sediment transport namely that sediment discharge is linearly proportional to the channel slope in accordance with the boundary and initial conditions imposed by the experimental setup and procedure the basic equation is amenable to an analytical solution which defines bed elevation at any distance and time as a function of the amount of base level lowering and a diffusion coefficient additional problems arising from bank erosion and channel armouring are also treated successfully within the framework of the same model the results show that in homogeneous alluvial sediments not subject to armouring the ultimate result of base level lowering by a certain amount is degradation all along the channel by the same amount the main impact of erosion is felt in the early stages after initiation of the process and mainly near the mouth the rate of degradation at any station along the channel reaches a peak and then slowly decreases with time and the peak rate is attenuated with distance from the outlet the model permits the prediction of intermediate stages of profile development at any distance from the outlet and at different times

the chinamora batholith zimbabwe structure and emplacement related magnetic rock fabric abstract the origin of dome and keel structural geometries in archean granite greenstone terrains appears to lack any modern analogues and is still poorly understood the formation of these geometries is investigated using structural and anisotropy of magnetic susceptibility ams data for the chinamora batholith in zimbabwe the roughly circular shaped batholith is surrounded by ca 2 72 2 64 ga greenstones the batholith granitoid suites have been divided on the basis of their ages and fabric relationships into four distinct units i banded basement gneisses ii granodioritic gneisses iii equigranular granites and iv central porphyritic granites in the gneissic granites a partial girdle n s of poles to the magnetic foliation is developed that has been folded around a consistent flat lying magnetic lineation plunging at shallow angles to the e or w in the equigranular granites the magnetic lineation generally plunges to the nw the magnetic foliation has a variable strike no clear trends can be distinguished the ams measurements of the porphyritic granite revealed a nw se striking foliation and showed subhorizontal magnetic lineations the magnetic foliation is subparallel to the macroscopic foliation wall rocks are moderately inclined and show radial or concentric lineations triaxial strain ellipsoids and kinematics that demonstrate off the dome sliding and coeval pluton expansion the results of the observations do not point to a single emplacement process neither the observed structural data nor the magnetic fabric support a model envisaging spherically ballooning it is argued that pluton diapirism played a major part in the formation of the fabrics in the gneisses whereas the fabrics in the porphyritic granites reflect emplacement as laccolith like sheets

structurally controlled drainage basin development in the south of menorca western mediterranean spain abstract the south of menorca consists of a gently folded upper miocene carbonate platform over which a drainage system has developed three areas with different drainage characteristics have been delimited the central area the eastern area and the western area the central area is characterised by deep streams with steep slopes whereas the western and eastern areas have slightly incised streams with gentle slopes the drainage development has been controlled by the inversion of a normal fault in pliocene times resulting in a wide anticline with a nne ssw orientation the deep streams of the central area follow the faults associated with this anticline the amount of incision achieved by these streams depends on the proportion of impermeable rocks exposed in the drainage basin the streams draining basins with a large proportion of impervious rocks have concave longitudinal profiles whereas those from catchments with a smaller area of impermeable materials have concave convex profiles streams with minor incision are found in the western and eastern areas of the carbonate platform given that their drainage basins are constituted by permeable materials

change in the mathematical function type describing the longitudinal profile of a river through an evolutionary process japanese rivers where a large amount of sediment accumulates along the middle reaches are today not at grade nevertheless most of their longitudinal profiles can be described by one of the mathematical functions proposed for graded rivers for these rivers the mathematical function should show an aspect of fluvial processes different from the explanations of grade theories the geomorphological significance of differences in the mathematical functions describing the longitudinal profiles of rivers is discussed here a dynamic change in the shape of longitudinal profile of a river accompanying the change in mathematical function type is proposed in relation to changes in fluvial processes and stage of evolution of a river most japanese rivers can be described by either exponential or power functions the fluvial processes of the rivers described by exponential functions are in the depositional state the front of depositional area of gravels increases in altitude and migrates downstream the rivers exp

multistage au as sb mineralization and crustal scale fluid evolution in the kwekwe district midlands greenstone belt zimbabwe a combined geochemical mineralogical stable isotope and fluid inclusion study the kwekwe district comprises the central part of the archean midlands greenstone belt of zimbabwe and represents one of few archean gold provinces in the world hosting gold deposits associated with massive antimony mineralization the deposits typically occur along late archean transcrustal deformation zones mineralization is characterized by an early au as stage 1 followed by a pronounced au sb stage 2 and a low grade sb bearing stage 3 four gold deposits within the kwekwe district have been studied the primrose and globe and phoenix gold deposits display typical features of archean orogenic lode gold systems such as fluid inclusions with low salinity mixed aqueous carbonic fluids formation temperatures between 300 and 400 c and a common stable isotope composition of fluid and mineral precipitates deposits of this type formed in the brittle ductile crustal transition zone at 1 5 to 3 0 kbars in contrast gold mineralization at jojo and especially the indarama gold deposits probably formed at lower temperatures 300 c and from dominantly aqueous early moderate to late high salinity fluids at indarama microthermometric studies indicate stibnite gold mineralization at temperatures between 120 and 230 c at about 0 8 to 1 8 kbars low formation temperatures and extremely low 34s values of pyrite 52 and stibnite 36 of the latest mineralization stage at indarama reveal reactivation of the hydrothermal system within a near subsurface organic rich epithermal or hot spring type environment during the late archean or even early proterozoic such low 34s values have not been reported previously from gold deposits in archean greenstone belts we propose that hydrothermal activity and gold mineralization has not only taken place at different crustal levels but also at different times

a geomorphological approach to determining the neogene to recent tectonic deformation in the coastal cordillera of northern chile atacama the large 10000 km2 and local scale 300 m sedimentary succession was deposited east of the afs the succession fills previously deep paleovalleys and it consists of gravel so called atacama gravels which passes laterally into fine grained playa related deposits near the afs we interpret the deposition of this succession as a result of a blocking closure of the valley flowing from the precordillera due to the activity on afs a pedimentation episode followed sediment deposition and is locally strongly re incised by the main modern day river valleys draining the precordillera incision may result from either regional uplift of the forearc and or from more localized activity on the afs furthermore recent quaternary tectonic activity on the afs has been observed which is consistent with a localized relative uplift of the crustal block west of the afs

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

fluvio marine sediment partitioning as a function of basin water depth progradational fluvio deltaic systems tend towards but cannot reach equilibrium a state in which the longitudinal profile does not change shape and all sediment is bypassed beyond the shoreline they cannot reach equilibrium because progradation of the shoreline requires aggradation along the longitudinal profile therefore progradation provides a negative feedback unless relative sea level falls at a sufficient rate to cause non aggradational extension of the longitudinal profile how closely fluvio deltaic systems approach equilibrium is dependent on their progradation rate which is controlled by water depth and downstream allogenic controls and governs sediment partitioning between the fluvial deltaic and marine domains here six analogue models of coastal fluvio deltaic systems and small prograding shelf margins are examined to better understand the effect of water depth subsidence and relative sea level variations upon longitudinal patterns of sediment partitioning and grain size distribution that eventually determine large scale stratigraphic architecture fluvio deltaic systems prograding in relatively deep water environments are characterized by relatively low progradation rates compared to shallow water systems this allows these deeper water systems to approach equilibrium more closely enabling them to construct less concave and steeper longitudinal profiles that provide low accommodation to fluvial systems glacio eustatic sea level variations and subsidence modulate the effects of water depth on the longitudinal profile systems are closest to equilibrium during falling relative sea level and early lowstand resulting in efficient sediment transport towards the shoreline at those times additionally the strength of the response to relative sea level fall differs depending on water depth in systems prograding into deep water relative sea level fall causes higher sediment bypass rates and generates significantly stronger erosion than in shallow water systems which increases the probability of incised valley formation water depth in the receiving basin thus forms a first order control on the sediment partitioning along the longitudinal profile of fluvio deltaic systems and the shelf clinoform style it also forms a control on the availability of sand grade sediment at the shoreline that can potentially be remobilized and redistributed into deeper marine environments key findings are subsequently applied to the literature of selected shelf clinoform successions

synthetic river valleys creating prescribed topography for form process inquiry and river rehabilitation design abstract the synthesis of artificial landforms is complementary to geomorphic analysis because it affords a reflection on both the characteristics and intrinsic formative processes of real world conditions moreover the applied terminus of geomorphic theory is commonly manifested in the engineering and rehabilitation of riverine landforms where the goal is to create specific processes associated with specific morphology to date the synthesis of river topography has been explored outside of geomorphology through artistic renderings computer science applications and river rehabilitation design while within geomorphology it has been explored using morphodynamic modeling such as one dimensional simulation of river reach profiles two dimensional simulation of river networks and three dimensional simulation of subreach scale river morphology to date no approach allows geomorphologists engineers or river rehabilitation practitioners to create landforms of prescribed conditions in this paper a method for creating topography of synthetic river valleys is introduced that utilizes a theoretical framework that draws from fluvial geomorphology computer science and geometric modeling such a method would be valuable to geomorphologists in understanding form process linkages as well as to engineers and river rehabilitation practitioners in developing design surfaces that can be rapidly iterated the method introduced herein relies on the discretization of river valley topography into geometric elements associated with overlapping and orthogonal two dimensional planes such as the planform profile and cross section that are represented by mathematical functions termed geometric element equations topographic surfaces can be parameterized independently or dependently using a geomorphic covariance structure between the spatial series of geometric element equations to illustrate the approach and overall model flexibility examples are provided that are associated with mountain lowland and hybrid synthetic river valleys to conclude recommended advances such as multithread channels are discussed along with potential applications

timing of skarn deposit formation of the tonglushan ore district southeastern hubei province middle lower yangtze river valley metallogenic belt and its implications abstract the tonglushan ore district in the middle lower yangtze river valley metallogenic belt includes the tonglushan cu fe the jiguanzui au cu and the taohuazui au cu skarn deposits they are characterized by ne striking ore bodies and hosted at the contact of triassic carbonate rocks and late mesozoic granitoid deposits new sensitive high resolution ion microprobe shrimp and laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb molybdenite re os and phlogopite 40 ar 39 ar ages indicate that these skarn deposits formed between 140 3 1 1 and 137 3 2 4 ma these dates are identical to the zircon u pb ages for host quartz diorites ranging from 140 2 to 139 1 ma these results confirm that both skarn mineralization and related intrusions were initiated during the early cretaceous the high rhenium contents 261 4 1152 g g of molybdenites indicate that a metasomatic mantle fluid was involved in the ore forming process of these skarn ore systems this conclusion is consistent with previously published constraints from sulfur deuterium and oxygen isotope compositions and the geochemical signatures and sr nd isotopic data of the mineralization hosting intrusions geological and geochronological evidence demonstrates that there were two igneous events in the tonglushan ore district the first resulted in the emplacement of quartz diorite during the early cretaceous 140 2 to 139 1 ma and the second is characterized by the eruption of volcanic rocks during the mid early cretaceous 130 2 to 124 2 ma the former is spatially temporally and genetically associated with skarn gold bearing mineralization 140 3 1 1 to 137 3 2 4 ma the recognition of these two igneous events invalidates previous models that proposed continuous magmatism and associated mineral deposits in the middle lower yangtze river valley metallogenic belt

gis analysis of depositional slope change at alluvial fan toes in japan and the american southwest abstract slope change at alluvial fan toes provides a clue to understanding differences between alluvial fans and other depositional landforms this paper analyses topographic data for 430 alluvial fans and their adjacent lowlands in japan and the american southwest asw typical humid and arid regions with abundant alluvial fans arcs showing fan toes were identified and representative areas above and below each arc were then delineated based on a gis buffer analysis the mean slope of the area above sa and below the fan toe sb and the ratio of sa to sb rs were computed overall fan slope so total fan length l and angle of the fan apex af were also measured relationships among these morphometric parameters reflect differences in climate and sedimentary processes fans in the asw tend to have straight profiles with similar values for sa and so indicating that fan gradients from deposition resulted from low frequency high magnitude storms have been preserved well under an arid climate higher rs values result from good preservation of both steep fan surfaces and gentle adjacent lowlands which is also ascribable to infrequent sediment redistribution in japan sa tends to be smaller than so and rs is often close to unity reflecting frequent sediment redistribution on fans and across fan toes under a humid climate rs in both the regions tends to converge into unity with increasing l longer alluvial fans are more strongly dominated by fluvial processes than by mass flows especially at their toes longer fans also tend to have small af leading to fluvial processes similar to those on floodplains sediment re mobilisation at the toes of such fans is more frequent resulting in smaller differences between sa and sb

macflincor and its application to fluids in archean lode gold deposits abstract macflincor was developed to process laboratory data gathered on fluid inclusions and to calculate isochores for geologically important fluids composed of h2o c02 ch4 nacl and n2 within the program interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically the user can choose from various published equations of state describing fluid behavior and can easily compare the results obtained by using different equations the program once the basic fluid parameters have been established allows the data to be used to determine the p t trapping conditions to evaluate possible pressure corrections and to compare different depths of formation based on the pressure calculations and given geothermal gradients for illustrative purposes macflincor has been utilized here to constrain different physical chemical parameters of fluid inclusions trapped in ore related quartz veins and breccias of archean lode gold deposits in western australia inferred pressures from individual deposits show a wide range of values which may be due to post entrapment modifications and or observational uncertainties including estimation of liquid vapor ratios

downstream fining in large sand bed rivers abstract downstream fining of bed sediments is a well known phenomenon in gravel bed rivers but also occurs in large sand bed rivers the underlying processes however are not necessarily the same due to the difference in sediment mobility grain size distribution width and geographical setting downstream fining studies focusing on large sand bed rivers are scarce nevertheless in this paper the processes that affect downstream fining in gravel bed rivers are reviewed and it is evaluated to what extent they are relevant for large sand bed rivers furthermore several new downstream fining processes are discussed ending in a conceptual model of downstream fining in large sand bed rivers in deriving the conceptual model downstream fining processes are divided into three categories abrasion selective transport and sediment addition extraction abrasion rates in large sand bed rivers are small due to the durable lithologies the small grain size the high degree of rounding the dominance of grinding as abrasion process and the dominant suspended transport mode of the bed sediment only in the upstream part of large sand bed rivers abrasion rates may be somewhat higher selective transport rates in large sand bed rivers everywhere overrun abrasion rates but are small compared to selective transport rates in gravel bed rivers because the unimodal sediments in sand bed rivers exhibit stronger hiding exposure effects during threshold of motion conditions but especially because many sand bed rivers though not all are in state of fully mobilised transport making differences in threshold of motion between coarse and fine grains relatively unimportant selective transport in these rivers is probably mainly the result of the presence of suspended load transport in combination with the effects of dune and perhaps bend sorting which are all processes that act on a relatively large scale within sand bed rivers the degree of selective transport probably decreases downstream due to the change in mixture bimodality and sorting efficiency there are indications that coarse grains may sometimes even be more mobile than fine grains in the downstream part of sand bed rivers note that in contrast to abrasion selective transport only produces a stable downstream fining pattern if the river profile is concave generally a stronger profile concavity leads to a higher aggradation rate and a stronger downstream fining trend sediment addition and extraction processes can obscure the effects of abrasion and selective transport in sand bed rivers overbank sedimentation for instance may significantly decrease the downstream fining rate in large sand bed rivers because especially fine grains are removed from the bed dredging can also strongly affect the downstream fining trend depending on the volume and the grain size of the sediment involved meander migration may cause a nett loss of coarse grains from the channel in aggrading circumstances increasing the downstream fining rate river bifurcations can cause a discontinuity in the downstream fining pattern because bend sorting upstream of the bifurcation causes the river branch that originates in the outer bend of the main channel to be much coarser than the other branch all these addition and extraction processes not only have a direct effect on the grain size composition of the river bed but also indirectly influence downstream fining by their effect on the longitudinal bed profile other sediment addition and extraction processes such as tributary confluences non alluvial sediment sources and dumping are less common in large sand bed rivers but can locally have a great effect a full determination of the relative importance of all downstream fining processes in large sand bed rivers requires extensive field measurements the construction of detailed fractionwise sediment balances and the development of numerical downstream fining models that incorporate all processes described above

geology mineralization stable isotope and fluid inclusion characteristics of the vostok 2 reduced w cu skarn and au w bi as stockwork deposit sikhote alin russia abstract the large 180 kt wo 3 and at least 10 15 t au vostok 2 deposit is situated in a metallogenic belt of w sn w au and au w deposits formed in late to post collisional tectonic environment after cessation of active subduction the deposit is related to an ilmenite series high k calc alkaline plutonic suite that by its petrologic signatures is transitional between those at w dominant and au dominant reduced intrusion related deposits consistently besides large w cu skarns of the reduced type the deposit incorporates quartz stockworks with significant au w bi mineralization also formed in a reduced environment the hydrothermal stages include prograde and retrograde essentially pyroxene skarns hydrosilicate amphibole chlorite quartz alteration and phyllic quartz sericite albite apatite and carbonate alteration assemblages these assemblages contain abundant scheelite associated with pyrrhotite chalcopyrite and at the phyllic stage also with bi minerals as bi sb te pb zn sulfides and sulfosalts as well as au mineralization the fluid evolution included hot high pressure 420 460 c 1 1 1 2 kbar low salinity 5 4 6 0 wt nacl equiv aqueous fluids at the retrograde skarn stage followed by lower temperature cyclic releases of high carbonic low salinity to non carbonic moderate salinity aqueous fluids at the hydrosilicate stage a high carbonic ch 4 dominated hot 350 380 c low salinity fluid was followed by cooler 300 350 c non carbonic moderate salinity 5 7 14 9 wt nacl equiv fluid at the phyllic stage a high carbonic co 2 dominated moderately hot 330 355 c 0 9 kbar low salinity fluid was followed by cooler 230 265 c non carbonic moderate salinity 6 6 12 0 wt nacl equiv fluid a homogenized magmatic source of water 18 o h2o 8 3 to 8 7 and a sedimentary source of sulfur 34 s 6 9 to 6 2 and carbon 13 c fluid 20 1 to 14 9 at the hydrosilicate stage are suggested a magmatic source of water 18 o 8 6 to 9 2 and a sedimentary source of sulfur 34 s 9 3 to 4 1 but a magmatic mantle to crustal derived source of carbon 13 c fluid 6 9 to 5 2 are envisaged for fluids that formed the early mineral assemblage of the phyllic stage then the role of sedimentary carbon again increased toward the intermediate 13 c fluid 16 4 to 14 5 and late 13 c fluid 16 3 to 14 7 phyllic mineral assemblages the magmatic differentiation was responsible for the fluid enrichment in w whereas au and bi could also have been sourced from mafic magma the decreasing temperatures together with elevated ca content in non boiling fluids promoted scheelite deposition at the early hydrothermal stages the most intense scheelite deposition at the phyllic stage was caused by co 2 removal due to boiling of co 2 rich fluids further cooling of non boiling fluids favoured joint deposition of scheelite bi and au

geology mineralization and fluid inclusion characteristics of the kumbel oxidized w cu mo skarn and au w stockwork deposit in kyrgyzstan tien shan the kumbel deposit is located within a metallogenic belt of w mo cu mo au w and au deposits along the late paleozoic active continental margin of tien shan the deposit is related to a late carboniferous multiphase pluton with successive intrusive phases from early olivine monzogabbro through monzonite quartz monzonite to granodiorite and granite with the latest monzogabbro porphyry dikes the deposit represents an example of a complex w cu mo au magmatic hydrothermal system related to magnetite series high k calc alkaline to shoshonitic igneous suite it contains large bodies of w cu mo oxidized prograde and retrograde skarns with abundant andradite garnet magnetite and especially hematite as well as k feldspar molybdoscheelite chalcopyrite and molybdenite with transitions to zones of intense quartz k feldspar with minor andradite and hematite veining the skarns are cut by quartz carbonate adularia sericite veins locally sheeted and stockworks bearing scheelite and minor cu zn pb sulfides as well as au bi te and as mineralization the association of these veins with the oxidized skarns and magnetite series intrusion is consistent with the general oxidized intrusion related w mo cu au type of deposit with an affinity to the alkalic silica saturated cu au mo porphyry deposits the fluid inclusion data show the predominance of magmatic hydrothermal aqueous chloride fluid during the formation of skarns and quartz carbonate scheelite sulfide veins the high fluid pressures 1 750 bars together with their high temperature up to 600 c and high salinity 50 60 wt nacl equiv suggest the formation of skarns and quartz k feldspar andradite hematite veins under conditions typical of magmatic hydrothermal transition depth of 4 5 km of intrusion related mineralized system possibly by exsolution of the fluids from crystallizing magma the auriferous quartz carbonate scheelite sulfide veins formed from high to moderate salinity from 40 to 20 wt nacl equiv and high pressure from 1 200 bars to 850 900 bars aqueous chloride fluids under decreasing temperature from 370 to 120 c the massive deposition of molybdoscheelite in retrograde skarn and scheelite in quartz carbonate scheelite sulfide veins could correspond to enrichment of fluids in ca up to 18 25 wt cacl2 likely from crystallizing magma