elemental and sr nd isotopic geochemistry of permian emeishan flood basalts in zhaotong yunnan province sw china this study presents new whole rock elemental and isotopic data for the basalts from the zhaotong area located in the intermediate zone of the 260 ma emeishan large igneous province elip the zhaotong basalts belong to high ti series with tio2 from 2 93 to 5 26 and ti y from 519 to 974 the parental magma was subjected to minor crustal contamination as indicated by slight nb ta depletion nb la 0 72 1 10 meanwhile the relatively invariable sr nd isotopes end t 0 74 to 2 86 mostly 1 10 to 2 86 87sr 86sr i 0 7050 0 7072 and the light rare earth elements lree enrichment la yb 10 3 19 1 of the basalts prefer a mantle plume origin a garnet dominated peridotite mantle source was further suggested on the basis of the ree distribution patterns and high sm yb and high la yb ratios this study further confirms the geochemical zoning of the high ti basalts in the elip which is in accordance with both the spatial distribution and the thickness of the basalts the high ti basalts in the intermediate and outer zones of elip e g zhaotong and guizhou share similar sr nd isotopic and elemental compositions suggesting that they originated directly from the emeishan mantle plume by contrast the high ti basalts in the inner zone e g longzhoushan and binchuan have variable compositions indicating a rather heterogeneous mantle source possibly involved with subcontinental lithospheric mantle sclm components

avulsion processes at the terminus of low gradient semi arid fluvial systems lessons from the rio colorado altiplano endorheic basin bolivia abstract the rio colorado dryland river system in the southeast of the endorheic altiplano basin bolivia terminates on a very flat coastal plain at the edge of the salar de uyuni the world s largest salt pan with an area of ca 12 500 km 2 since the pleistocene the basin has experienced several lake expansion and contraction cycles in response to wetter and drier climate periods respectively at present the basin is in a dry climate period which results in a lake level lowstand and progradation of fluvial systems such as the rio colorado onto the former lake bottom the present field study of the terminus of the rio colorado shows that the river experiences a gradual downstream decrease of bankfull width and depth this bankfull decrease is caused by the combined effects of 1 extremely low gradient of the lake bottom and hence loss of flow energy and 2 downstream transmission losses due to high evaporation potential and river water percolation through the channel floor peak water discharge in seasonal short duration rain periods causes massive overbank flooding and floodplain inundation on satellite images the morphology of the river terminus has a divergent pattern and resembles a network of coeval sinuous distributary channels however field observations show that only one channel is active at low flow stage and at high flow stage an abandoned partially infilled channel may be active as well the active channel at its termination splits into narrow and shallow anastomosing streams before its demise on the lacustrine coastal plain the rest of the channels which form the divergent network are older sediment filled abandoned sinuous river courses with multiple random avulsion points these channel deposits together with extensive amalgamated crevasse splay deposits form an intricate network of fluvial sand deposits successive stages of progressively deeper crevasse channel incision into the floodplain are the result of waning stage return flow of floodwaters towards the main channel this results in increased crevasse channel width depth and length and redeposition of eroded lacustrine coastal plain sediment at the junction of the crevasse channel with the present day river a sedimentary model is proposed in which deep river bank incision by return flow in crevasse channels creates the preferential locus for river avulsion in a lowstand systems tract with little vertical accommodation increase the recurring avulsed river paths result in a thin but laterally extensive network of amalgamated channel fill point bar crevasse channel and crevasse splay deposits the resulting sedimentary architecture could easily be mistaken as produced by a distributary system of simultaneously active fluvial channels

two magma series and associated ore deposit types in the permian emeishan large igneous province sw china the late middle permian 260 ma emeishan large igneous province in sw china contains two magmatic series one comprising high ti basalts and fe rich gabbroic and syenitic intrusions the other low ti basalts and mafic ultramafic intrusions the fe rich gabbros are spatially and temporally associated with syenites each series is associated with a distinctive type of mineralization the first with giant fe ti v oxide ore deposits such as panzhihua and baima the second with ni cu pge sulfide deposits such as jinbaoshan limahe and zhubu new shrimp zircon u pb isotopic data yielded 263 3 ma for the limahe intrusion 261 2 ma for the zhubu intrusion and 262 2 ma for a syenitic intrusion these new age dates together with previously reported shrimp zircon u pb ages suggest that all these intrusions are contemporaneous with the emeishan flood basalts and formed during a major igneous event at ca 260 ma the oxide bearing intrusions have higher al2o3 feo as total iron and total alkalis na2o k2o but lower mgo than the sulfide bearing intrusions all intrusions are variably enriched in lree relative to hree the oxide bearing intrusions display positive nb and ti anomalies and in certain cases negative zr hf anomalies whereas the sulfide bearing intrusions have obvious negative nb and ti anomalies a feature of crustal contamination individual intrusions have relatively small ranges of nd t values all the intrusions however have nd t values ranging from 3 9 to 4 6 and initial 87sr 86sr ratios from 0 7039 to 0 7105 the syenites have very low mgo 2 wt but highly variable fe2o3 2 5 to 13 wt with initial 87sr 86sr ratios ranging from 0 7039 to 0 7089 magmas from both series could have derived by melting of a heterogeneous mantle plume the high ti series from a fe rich more fertile source and the low ti series from a fe poor more refractory source in addition the low ti series underwent significant crustal contamination the two magma series evolved along different paths that led to distinct mineralization styles

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

chemical weathering of volcanic rocks at the island of pantelleria italy information from soil profile and soil solution investigations abstract concentrations of major minor and trace elements were determined in soil profiles and soil solutions from the island of pantelleria sicily channel to evaluate the weathering extent of soils evolved on trachytic and pantelleritic rocks and the aqueous transport of elements by their soil solutions the chemical index of alteration cia indicates a low to moderate degree of weathering consistently the mineralogical and geochemical imprints of the parent rocks are generally preserved the chemical weathering appears to be incongruent owing to primary minerals and glass dissolving to a variable degree while secondary minerals have formed based on the calculated saturation state of primary and secondary minerals with respect to the soil solutions and on mineralogical observations olivine and pyroxene are unstable and dissolving whereas magnetite and hematite are stable the main weathering products are amorphous phases such as ferrihydrite amorphous aluminium hydroxide and silica clay mineral formation appears to be incipient and mainly limited to kaolinite and smectite although for some soil profiles a hydrothermal origin is suggested for these minerals chemical characteristics of soil solutions and elemental mobility are controlled by the element source and water rock interaction

zircon u pb geochronology and elemental and sr nd isotope geochemistry of permian mafic rocks in the funing area sw china mafic layered intrusions and sills and spatially associated andesitic basalts are well preserved in the funing area sw china the 258 3 ma layered intrusions are composed of fine grained gabbro gabbro and diorite the 260 3 ma sills consist of undifferentiated diabases both the layered intrusions and volcanic rocks belong to a low ti group whereas the diabases belong to a high ti group rocks of the high ti group have feo tio2 and p2o5 higher but mgo and th nb ratios lower than those of the low ti group they have initial 87sr 86sr ratios 0 706 0 707 lower and nd 1 5 to 0 6 higher than the low ti equivalents 0 710 0 715 and 9 6 to 4 0 respectively the high ti group was formed from relatively primitive high ti magmas generated by low degrees 7 3 9 5 of partial melting of an enriched oib type asthenospheric mantle source the low ti group may have formed from melts derived from an em2 like lithospheric mantle source the mafic rocks at funing are part of the emeishan large igneous province formed by a mantle plume at 260 ma

trace element and sr nd isotopic geochemistry of the pge bearing xinjie layered intrusion in sw china abstract the xinjie layered intrusion is one of a number of major ultramafic mafic bodies hosting fe ti v deposits and cu ni pge sulfide in the pan xi area of the sichuan province sw china the intrusion is a 7 5 km long 1 to 1 5 km wide and 1200 m thick ultramafic mafic sill which is associated with permian plume related emeishan flood basalts the intrusion is characterized by three lithological cycles each representing a sequence from ultramafic to basic felsic composition the basal part of the intrusion is composed of three lithological units namely the marginal peridotite and pyroxenite units two major pge mineralized layers occur within the marginal and pyroxenite units the marginal unit mu is characterized by marked nb ta sr and ti enrichments and obvious th depletion while the peridotite unit peu shows significant sr slight zr depletion and pronounced positive ti anomalies the pyroxenite unit pyu is depleted in nb and zr but significantly enriched in sr and ba with lower ratios of nb la and zr sm compared to those of the underlying two units the pge enriched layer in the marginal unit has elevated and highly variable rb la and ba th values and the lower part of the pyroxenite unit which includes a pge enriched layer exhibits high and decreasing rb la and ba th ratios upwards sr nd isotopic compositions of samples from the three units ca 90 m thick were systematically analyzed and fall in a range of 0 7056 to 0 7074 for 87sr 86sr i and of 5 26 to 2 79 for end i within the marginal and peridotite units high 87sr 86sr i and low end i values are demonstrated by contrast an enriched sr isotopic 87sr 86sr i 0 7074 and slightly depleted nd isotopic end i 2 5 signature occurs in the basal pyroxenite unit 8 m below the pge enriched layer in this unit the marginal unit is interpreted as the product of contamination of a plume component e g end i 5 and 87sr 86sr i 0 704 by continental crust the peridotite unit has undergone decreasing degrees of crustal contamination at the bottom of the pyroxenite unit a new magma input contaminated by upper crust is proposed where its slight nd sr decoupling may be attributed either to the much higher sr content than the nd content of the contaminant or the selective contamination of sr rather than nd the pge mineralization in the pyroxenite unit was caused by magma mixing between the new magma and the resident magma whereas the pge enriched layer in the marginal unit resulted from wallrock contamination however the displacement of the isotopic pulse from the pge enriched layer in the pyroxenite unit is due to later sulfide saturation being achieved in both end members both of the pge enriched layers are linked directly to the segregations of the fe ti oxides and sulfides

unconfined flow deposits in distal sectors of fluvial distributary systems examples from the miocene luna and huesca systems northern spain abstract thin sheet sandstone beds in a continental succession may be the products of unconfined overbank flow or deposition in lacustrine environments in the distal parts of fluvial distributary systems these two settings may be intercalated recording fluctuations in lake level in response to climatic changes field studies of the luna and huesca fluvial distributary systems in the miocene of the ebro basin spain are here used to characterise sheet sandstone deposited in distal fluvial and lake margin environments in this study we document the facies and relationships between 322 individual sandbodies deposited in both alluvial settings as sheetfloods and in lacustrine settings as deltaic lobes the alluvial sandstone sheets were deposited from lateral and frontal sheetflood events when unconfined flow replaced channelised flow as the main transport mechanism the term sheetflood is used here to refer to sub aerial unconfined turbulent flow events that undergo expansion thinning and deceleration with increasing radial distance from source the depositional process is similar to modern floodouts and terminal splays of the channel country and lake eyre central australia such a process was thought to be the dominant depositional mechanism during lake lowstands the sheets formed in the lacustrine setting are interpreted as deltaic sediments deposited in a shallow gradient lake similar to the modern day volga delta caspian sea shallow water friction dominated deltaic processes are thought to have been the primary depositional mechanism in the distal sectors of the fluvial systems during lake highstands

high resolution sequence stratigraphy of fluvio deltaic systems prospects of system wide chronostratigraphic correlation a basin scale numerical model with a sub grid parameterization of fluvio deltaic processes and stratigraphy was used to study the relation between alluvial sedimentation and marine deltaic deposition under conditions of time invariant forcing the experiments show that delta evolution is governed by a robust morphodynamic feedback loop which provides a link between major avulsions delta lobe switches and sequestration of sediments on the delta plain major avulsions driven by local superelevation result in abandonment of delta lobes and initiation of new lobes progradation of the delta front lengthens the fluvial profile and reduces its gradient which induces aggradation upstream the aggradation in turn causes local superelevation of the channel belt each major avulsion causes a wave of incision to migrate upstream whereas downstream of the avulsion point the rate of aggradation temporarily increases until a new equilibrium situation has been established the feedback loop explains storage and release of fluvial sediments without the need to invoke changes in upstream or downstream controls and provides a plausible mechanism for the generation of high frequency incision aggradation cycles as the sole result of compensational stacking the stratigraphic expression of a depocentre shift is an essentially isochronous surface hence the stratigraphic record of fluvio deltaic systems may be subdivided into a series of units representing intervals during which a channel belt and delta lobe were forming at a fixed location in the basin so called chronosomes fluvio deltaic chronosomes are bounded by abandonment surfaces which are clearly expressed in the marine as well as the fluvial domain the surface marking the abandonment of a particular channel belt and delta lobe correlates with the surface at the base of a new delta lobe landward this surface forms the base of an aggradational package of fluvial sediments downstream of an avulsion site associated with a lobe switch upstream of this site the conformable surface passes into a surface of fluvial incision and terrace formation onlapped by aggradational channel belt deposits identification of the isochronous bounding surfaces of chronosomes in the field offers the attractive prospect of high resolution chronostratigraphic correlation throughout fluvio deltaic systems

longevity of the permian emeishan mantle plume sw china 1 ma 8 ma or 18 ma after the formation of the 260 ma emeishan large igneous province there were two volumetrically minor magmatic pulses at 252 ma and 242 ma respectively alkaline mafic dykes intruding both 260 ma and 252 ma felsic plutons in the panxi region southwestern china have compositions similar to the emeishan flood basalts one dyke is dated using the shrimp zircon u pb technique at 242 2 ma 18 ma younger than the start of emeishan magmatism the dykes have enriched light rare earth element patterns la ybn 4 4 18 8 and trace element patterns similar to the emeishan flood basalts and average ocean island basalts some trace element ratios of the dykes zr nb 3 8 8 2 la nb 0 4 1 7 ba la 7 5 25 6 are somewhat similar to em1 source material however there are differences their end values end 2 6 and 2 7 and i sr i sr 0 704542 and 0 704554 ratios are indicative of a mantle source thus emeishan magmatism may have lasted for almost 20 ma after the initial eruption however geological evidence precludes the possibility that the post 260 ma magmatic events were directly related to emeishan magmatism which began at and ended shortly after 260 ma the 252 ma plutons and 242 ma dykes represent volumetrically minor melting of the fossil emeishan plume head beneath the yangtze crust the 252 ma magmatic event was likely caused by post flood basalt extension of the yangtze crust whereas the 242 ma event was caused by decompressional melting associated with the collision between the south china and north china blocks during the middle triassic

ni cu pge magmatic sulfide deposits in the yangliuping area permian emeishan igneous province sw china the ni cu pge sulfide deposits in the yangliuping area sw china are hosted in mafic ultramafic sills the four mineralized sills are located in the yangliuping tectonic dome and intrude devonian carbonaceous marble graphitic schist the sills are 200 300 m thick and 1 000 2 000 m in strike length and now consist chiefly of serpentinite talc schist tremolite schist and meta gabbro disseminated ni cu sulfide mineralisation occurs in the serpentinite in the lower parts of the sills massive sulfide mineralisation is located in the base of the sills and in the footwall along fractures beneath the mineralized serpentinite although the sulfide ores have been modified by hydrothermal activity there are relict cumulate textures in the disseminated sulfides indicating a magmatic origin for the ores the yangliuping intrusions and the dashibao formation have similar primitive mantle normalized trace element and platinum group element pge patterns indicating that they are derived from a common parental magma type the positive correlation between cu concentrations and cu zr ratios of the dashibao formation basalts indicates that the chalcophile elements were removed before eruption we propose that fractional crystallization of the yangliuping magma accompanied by the introduction of s and co2 from the wall rocks caused the magma to become s saturated leading to the segregation of magmatic sulfides that became enriched in ni cu pge the sills acted as conduits for the overlying dashibao formation basalts with the sulfide liquid along with early crystallizing olivine and pyroxene segregating from the magma as it passed through the conduits prior to eruption

soils in the semi arid area of the el melah lagoon ne tunisia variability associated with a closing evolution abstract soils of the semi arid area of the el melah coastal lagoon ne tunisia with a closing evolution dynamic were studied aiming 1 the chemical and mineralogical characterization of surface and subsurface layers of soil profiles from locations previously submerged and of soils developed on dunes 2 to evaluate the dependence on the environment conditions of the geochemical patterns of the soils and 3 to determine chemical and mineralogical variations with the emersion of the sediments resulting from the decrease in the extent of the area permanently covered by water in the lagoon the compositional results obtained showed significant differences depending on the environment littoral plain old dunes and sandy spit but soils of the different environmental zones studied do not appear to be significantly polluted as far as trace elements are concerned among the elements studied high element sc ratios and variations were found for as sb and zn antimony is more concentrated in coarser samples suggesting its adsorption in fe or mn oxides coating quartz grain surfaces arsenic and zinc may be incorporated into the carbonates structure as well as adsorbed on or coprecipitated with iron oxides zinc may also be significantly incorporated in clay minerals iron was found to be more oxidized in the cultivated soil from the old dune strand and more reduced in the sandy spit where ankerite occurs suggesting the reduction of fe3 in oxide hydroxides by microorganisms and incorporation of fe2 in carbonates ree patterns particularly the hree lree are correlated with carbonates indicating preferential incorporation of the hree in carbonates and of the lree in clay minerals iron oxides high ga contents were found in soils and sediments rich in clay minerals al suggesting its incorporation in clay minerals structure therefore ga may be used as an indicator of the clay minerals proportion in sediments and soils carbonates sulphates besides fe and or mn oxides and clay minerals appear to play an important role on the trace elements distribution

iron speciation in volcanic topsoils from fogo island cape verde iron oxide nanoparticles and trace elements concentrations abstract iron contents its compounds and forms in topsoils of the volcanic fogo island cape verde were studied by neutron activation analysis mossbauer spectroscopy and x ray diffraction the topsoils were collected from all units of the island in diverse geological formations carbonatite nephelinites limburgite pyroclasts deposits pre historic lavas and historic lavas fine materials from mota gomes volcanic crater the most recent eruption which occurred in 1995 were also sampled the total iron content varies significantly from 1 7 fe2o3 weight in acid sulfate topsoils ph 3 9 up to between 9 9 and 20 6 in the other geological contexts ph 5 9 to 9 3 the most oxidized topsoils from the pre caldera formations are the oldest ones as expected while the reverse is observed for the post caldera topsoils in the latter case fast weathering of the lava outer layers which have a higher glass component may explain this observation after erosion periods of 50 200 years significant amounts of the highly oxidized small particles are removed the inner part of the lava less oxidized is then exposed and more slowly weathered than the former outer layers topsoils from pre caldera formations derived from the more weather resistant inner layers are also strongly altered since they have been exposed for periods of time several orders of magnitude longer than the post caldera ones in topsoils fe2 mainly occurs in pyroxenes phyllosilicates and pure or slightly oxidized magnetite with increasing age the fe2 total fe ratio of the pre caldera topsoils gradually decreases down to 4 indicating that the iron that is still incorporated in the silicates structures is increasingly oxidized maghemite is detected instead of magnetite and hematite appears becoming the main fe containing phase in the oldest materials these results suggest that in a first weathering step fe2 is oxidized within the silicates structure and within magnetite which gradually evolves to maghemite with the eventual decomposition of silicates fe3 is remobilized in hematite as weathering proceeds maghemite is also replaced by hematite goethite was not detected by mossbauer spectroscopy which may be explained by the aridity of the island iron in jarosite was identified by mossbauer spectroscopy in topsoils developed on volcanic conduits the presence of this mineral in alkaline surficial environments may be explained by a hypogene origin and stability over at least a few hundred years in the surficial environments of the semi arid fogo island contents of cr and as that are potentially harmful to health increase with the concentration of nanosized fe oxides this correlation may be related to their high specific surface area

noble gas isotopic systematics of fe ti v oxide ore related mafic ultramafic layered intrusions in the panxi area china the role of recycled oceanic crust in their petrogenesis olivine and clinopyroxene grains have been separated from four large fe ti v oxide ore bearing intrusions panzhihua hongge baima and taihe in the panxi area emeishan large igneous province southwest china for he and ar isotope studies the samples examined revealed extremely low 3 he 4 he ratios 0 078 4 34 ra with the mean value 0 78 ra for gases extracted by stepwise heating this feature combined with low 40 ar 36 ar ratios can be interpreted as due to addition of subduction related fluids and melts that had been stored in the lithospheric mantle for long periods considering the regional geologic history such addition can be attributed to the paleo subduction that occurred along the western margin of the yangtze block during the neoproterozoic the subducted oceanic crust beneath the panxi area underwent eclogite facies metamorphism and subsequent exhumation the infiltration of subduction related melts and fluids into the lithospheric mantle led to enriched isotopic signatures from that of the slightly depleted asthenopheric mantle which has been suggested by the sr nd and pb isotopic data of the emeishan basalts and picrites in addition considerable amounts of eclogitic melts produced by partial melting of eclogite facies oceanic crust extensively contaminated the lithospheric mantle during the late permian partial melting of an upwelling mantle plume that contained an eclogite or pyroxenite component generated the parental fe rich magma that supplied the ore bearing intrusions the combination of these factors may have been the crucial reason that many world class fe ti v oxides deposits are clustered in the panxi area

new constraints on the open magma chamber processes in the formation of giant hongge fe ti v oxide deposit abstract the hongge layered intrusion in emeishan large igneous province elip sw china contains the largest fe ti v oxide deposit in china 4500mt ore reserve the mechanism by which million tons of fe ti v oxide concentrated is debated in this study new petrography mineral chemistry 3600 microprobe analyses for olivine clinopyroxene and plagioclase and bulk rock major element chemistry 108 samples are presented from samples collected over a 940 m drill core zk11003 in the southern part of the hongge layered intrusion in contrast to the bushveld and skaergaard layered intrusions a broad normal fractionation trend upwards recorded by cumulus clinopyroxene and plagioclase is absent whereas frequent reversals to more primitive compositions are observed in the hongge intrusion according to the mineral reversals we divided the entire intrusion into eleven stratigraphic units notably in the middle zone mz and lower zone lz the appearance of fe ti v oxide ore layers are closely related to these reversals these distinct units are regarded as indicators for major replenishments of primitive high ti ferrobasaltic picritic magmas in these samples various clinopyroxene populations with both low and high mg are also observed and phases with high mg are interpreted to be inherited from the replenishing magmas previous studies have proposed that the replenishing magma might be anhydrous however the presence of a considerable amount of hydrous cumulus minerals including phlogopite and hornblende indicates that there is a high water content in melts at some stages of the formation of the hongge layered intrusion especially in the lz and mz contamination of crustal materials e g introduction of aqueous fluids or replenishing magmas with different water contents could lead to high water activities in the shallow crystallizing magma chamber as a consequence mixing of hydrous residual melts with replenishing magmas would trigger large scale precipitation of fe ti v oxide ores relatively high water activity which could suppress the crystallization of cumulus plagioclase would also explain the absence of this phase in the lz and mz thus based on all these observations we propose that the hongge layered intrusion was formed by multiple emplacements of crystal laden magmas that carried olivine and clinopyroxene already crystallized in deep seated chambers

platinum group element geochemistry of the hongge fe v ti deposit in the pan xi area southwestern china mafic and ultramafic intrusions in the pan xi area along the western margin of the yangtze block southwestern china are spatially associated with the late permian emeishan flood basalts of the emeishan large igneous province the hongge layered intrusion is one of the plutonic bodies of this province and hosts a giant fe v ti deposit this intrusion has three zones a lower olivine clinopyroxenite zone a middle clinopyroxenite zone and an upper gabbro zone each of these zones consists of one or two compositional cycles which have distinct mg values tio2 concentrations and total ree contents the middle clinopyroxenite zone and upper gabbro zone contain thick 14 84 m magnetite mineralized layers samples from the lower olivine clinopyroxenite zone and middle clinopyroxenite zone of the hongge intrusion are enriched in platinum and palladium relative to iridium and ruthenium rocks of the lower olivine clinopyroxenite zone have pd ir ratios 1 8 22 3 lower than those of the middle clinopyroxenite zone 6 2 to 83 in its lower part and 3 6 to 49 in its upper part the pd ir ratios increase progressively upwards in each cyclic unit chromite is the major phase controlling concentrations of iridium and ruthenium the cu pd ratios at the bottom of each cyclic unit are close to that of the mantle and increase upwards this variation suggests that each cyclic unit represents a new batch of magma and sulfide mineral segregation removes pge platinum group elements ni and cu each cyclic unit in the hongge layered intrusion might have resulted from crystal fractionation and mixing between a primary and evolved magma the high cu pd ti pd ni pd and cu ir ratios of the intrusion suggest that the sulfide mineral segregation may have played an important role in pge differentiation if this interpretation is correct then there is a potential to find economic pge rich horizon in the hongge type intrusions in the region

geochronology of layered mafic intrusions from the pan xi area in the emeishan large igneous province sw china the panzhihua xichang pan xi area hosts mafic ultramafic intrusions which are part of the permian emeishan large igneous province some of these intrusions host giant fe ti v deposits and minor ni cu pge mineralization in the present study zircon u pb ages of 259 3 1 3 and 260 7 0 8 ma have been obtained from the giant fe ti v ore bearing hongge and the unmineralized binggu intrusions respectively by isotope dilution thermal ionization mass spectrometry method in combination with the ages of other ore bearing intrusions this age shows that these mafic ultramafic intrusions were emplaced at ca 260 ma the hongge and binggu intrusions cut the lower part of the rapidly deposited emeishan flood basalt sequence but no further into the upper volcanic sequence in the pan xi area thus emplacement and mineralization of the mafic ultramafic intrusions were almost contemporaneous with the eruption of the emeishan flood basalts during a relatively short time span

basin scale changes in floodplain paleosols implications for interpreting alluvial architecture abstract floodplain paleosols in time equivalent strata of the willwood for mation differ in terms of paleodrainage and degree of pedogenic development ancient soils were more poorly drained and more strongly developed in one area compared to a second area about 45 km away this difference in drainage is attributed to parent material the more poorly drained paleosols formed in an area with less permeable clay rich floodplain deposits in the stratigraphic interval that accumulated more slowly paleosols are more strongly developed less numerous and thicker than in the more rapidly accumulating stratigraphic interval these differences are attributed not only to different sediment accumulation rates which are commonly considered to control the degree of ped ogenic development but also to differences in avulsion frequency a simple model is offered to show how paleosols change with varying basin subsidence rates and the relationship between avulsion frequency and accumulation rate when avulsion frequency increases more rapidly than sediment accumulation rate an increase in subsidence rate causes strongly developed paleosols to be overlain by a stratigraphic interval with paleosols that are less well developed thinner and more densely spaced when avulsion frequency is not related to accumulation rate as early models of alluvial architecture assumed an increase in subsidence rate produces a stratigraphic section in which strongly developed paleosols are overlain by paleosols that are less well developed thicker and more widely spaced study of the thickness and degree of development of floodplain paleosols can be used together with more traditional studies of alluvial architecture to provide a clearer understanding of the factors that influenced the stratigraphic architecture in a particular alluvial basin

abundant fe ti oxide inclusions in olivine from the panzhihua and hongge layered intrusions sw china evidence for early saturation of fe ti oxides in ferrobasaltic magma abundant fe ti oxide inclusions in cumulus olivine fo77 81 from the panzhihua and hongge intrusions emeishan large igneous province sw china document the first evidence for early crystallization of fe ti oxides in ferrobasaltic systems in nature the intrusions also contain significant stratiform fe ti v oxide ores the oxide inclusions are sub rounded or irregular range from 5 to 50 m in diameter and are dominated by either titanomagnetite or ilmenite the fact that the inclusions are either titanomagnetite or ilmenite dominant suggests that they are trapped crystals instead of immiscible oxide melt formed during growth of the host olivine the absence of other silicate phases in the inclusion bearing olivine is difficult to reconcile with a possible xenocrystic origin of the oxide inclusions these oxide inclusions are thus interpreted to be cumulus minerals crystallized together and trapped in olivine from the same parental magma in addition to fe ti oxides some inclusions contain amphibole biotite fluorapatite that might have formed by reaction of trapped hydrous liquid with the host olivine numerical modeling of high ti emeishan basalts using the melts program successfully simulates early crystallization of olivine fo81 and fe ti spinel in the presence of a moderate amount of h2o 1 5 wt under pressure and fo2 conditions generally pertinent to the panzhihua and hongge intrusions the modal mineralogy of the oxide inclusions is in good agreement with the bulk compositions of the ore as inferred from whole rock data in a given intrusion this is consistent with the interpretation that the stratiform oxide ores in the intrusions formed by accumulation of fe ti oxide crystals that appeared on the liquidus with olivine and clinopyroxene

a reappraisal of the high ti and low ti classification of basalts and petrogenetic linkage between basalts and mafic ultramafic intrusions in the emeishan large igneous province sw china abstract based on published data we reappraise the classification of high ti and low ti basalt from the emeishan large igneous province elip and the correlations between basalts and mafic ultramafic intrusions because of the lack of clear spatial and temporal variations of different types of basalts we suggest that the basalts in the elip cannot be classified into high ti and low ti groups by tio 2 contents and or ti y ratios the distinctive characteristics of these high ti and low ti lavas probably result largely from the different fractionating assemblages whether or not fractional crystallization of the fe ti oxides occurred probably is the key factor that controls the ti abundances and ti y ratios in the residual melts e g lavas although the nature of the mantle sources variable degrees of partial melting of mantle and crustal contamination also influence the geochemical signatures of the lavas therefore neither ti abundance nor ti y ratios in basalts can reflect the nature of their mantle source moreover the different types of mafic ultramafic intrusions in the elip cannot simply be attributed to be genetically related special types of basalts either high ti or low ti basalts it is likely that they are merely the cumulus phases i e chamber or conduit of the basaltic lavas hence caution should be exercised in the use of high ti or low ti basalts as prospecting vectors for ore deposits in the region potential implications are proposed that both the fe v ti oxide and cu ni pge sulfide mineralization in the elip intrusions is largely due to the variable differentiation and crustal contamination during magmatic processes

integrated gis based modelling for the quantitative prediction of magmatic ti v fe deposits a case study in the panzhihua xichang area of southwest china abstract the estimation of undiscovered mineral resources is an important part in the potential value of a mineral field and its long term use this manuscript documents six procedures for estimating the volume of potential mineral resources in an area that is based on integrated geological information forming part of a metallogenic model the technique for this methodology includes 1 the development a metallogenic model or models for mineral deposits in the study area 2 the integration of the characteristics of known mineral anomalies with geology geochemistry and geophysics to establish a predictive model for mineralization 3 the definition of possible mineral resources incorporating predictive models with characteristic analyses the knowledge driven delphi method and magnetic anomalies 4 calculate the parameters for the quantitative prediction areas of known mineral deposits and their estimated dip extension ore bearing coefficients and their similarity coefficients based on explored ore deposits in the area studied 5 complete quantitative predictions using an synthetic volumetric equation and 6 assess zones that are considered prospective for mineral resources the procedure is tested for magmatic ti v fe resources in a known mineralized zone in the sichuan province of china

geoavailability of lithogenic trace elements of environmental concern and supergene enrichment in soils of the sierra de aracena natural park sw spain abstract the chestnut grove soils of the sierra de aracena natural park sw spain are a striking example of geoavailability and pedochemical enrichment with geologically sourced trace elements notably zn pb ag and cd but also as sb cu and tl the data from this study provide evidence that such metal loid s were originally bound to reactive sulphides pyrite sphalerite and galena and ag sb pb sulfosalts residing in the soil parent rock at the early stages of weathering these geoavailable elements were easily liberated from the mineralised bedrock through oxidative dissolution reactions and then transferred to the soil thus reaching anomalously high concentrations the most extreme amounts of zn 12 26 g kg 1 pb 5 g kg 1 as 346 mg kg 1 cd 319 mg kg 1 cu 197 mg kg 1 ag 154 mg kg 1 sb 109 mg kg 1 and tl 82 mg kg 1 were measured in soils developed over carbonate hosted sulphide occurrences and their related gossan outcrops when compared to the regional pedogeochemical baseline the soils are largely enriched with all the elements analysed except co cr and ni yielding concentration factors particularly high for zn 50 8 cd 49 3 ag 30 6 sb 22 5 and pb 20 8 and geo accumulation indices that consistently point to strong geogenic contamination the pedochemical enrichment may be reasonably attributed to the combined result of precipitation as a solid phase e g zn vermiculite hemimorphite hydrozincite and plumbogummite and specific adsorption by soil constituents mainly organic matter and iron oxy hydroxides the survey area can be considered as a hot spot in terms of both valuable metal prospecting and environmental concern although the soil acted as a natural sink for lithogenic trace elements it could eventually turn into a source of potentially hazardous contaminants in response to future land use changes and biogeochemical alterations

latest oligocene late miocene lacustrine systems of the north central part of the ebro basin spain sedimentary facies model and palaeogeographic synthesis abstract in the central part of the ebro basin spain north of the ebro river three allostratigraphic or tectosedimentary units differentiated within the latest oligocene late miocene upper agenian vallesian interval are sedimentologically characterized these deposits represent carbonate and sulphate lacustrine environments fed by pyrenean alluvial systems luna system and huesca system in each unit several facies associations or lithofacies were mapped these interfinger through time gypsum lithofacies occupy the southernmost part of the study area and are surrounded by carbonate and or detrital lithofacies to the north each lithofacies consists of different carbonate sulphate and or detrital facies arranged in simple sequences decimetres to metres thick the four types of sequences characterized reflect a complex shallowing evolution involving carbonate or sulphate contexts thus each lithofacies represents the sedimentation in a particular lacustrine or alluvial subenvironment a single lacustrine system is proposed for the central part of the basin its evolution followed cycles of water level variations which caused kilometre scale migrations of the lake shoreline in this model two distinct situations or lakes alternated through time a one represents high levels associated with a single body of dilute carbonate water where massive carbonate facies formed influenced by organism proliferation these lakes had wide palustrine vegetated margins in which bioturbated facies developed b the other represents low levels that correspond to a playa lake model laminated sulphate deposits formed in the lake waters while nodular gypsum originated in the surrounding saline mud flats and within the exposed previously deposited carbonate sediments transitions from one situation to the other including minor water level fluctuations within carbonate sedimentation conditions were marked by the development of laminated and stromatolitic facies lake level variations were caused by climatic cycles and gave rise to the simple sequences and to the lithofacies lateral relationships recognized in this study correlation among tectosedimentary units in the studied pyrenean domain and in the iberian domain of the ebro basin shows that for units n1 and n2 the facies that resulted from dilute carbonate waters are rare in the lacustrine areas of the iberian margin this indicates that a strong hydrological contrast existed between both regions on this basis a theoretical asymmetrical facies model is proposed for the single lacustrine basin that extended over these regions

whole rock and mineral composition constraints on the genesis of the giant hongge fe ti v oxide deposit in the emeishan large igneous province southwest china the hongge giant fe ti v oxide ore deposit is hosted by a layered intrusion located in the central part of the emeishan large igneous province sw china the intrusion is relatively small in comparison with other typical oxide bearing intrusions worldwide it consists of a lower olivine clinopyroxenite zone a middle clinopyroxenite zone and an upper gabbro zone herein referred to as the lower middle and upper zones most of the economic fe ti v oxide ore layers occur within the middle zone the hongge oxide ores are depleted in ree and enriched in zr hf nb and ta as compared to the associated clinopyroxenites this enrichment of elements that are compatible in titanomagnetite is consistent with the interpretation that the ores formed by accumulation of magnetite and ilmenite as in the nearby coeval panzhihua fe ti v oxide deposit described previously by others mafic silicates in the hongge deposit have much higher mgo contents than those in other oxide deposits associated with large layered intrusions in the world this highlights the importance of relatively primitive parental magma becoming saturated in titanomagnetite at an early stage in the genesis of the giant fe ti v oxide deposits in the emeishan large igneous province phase equilibrium constraints suggest that the parental magma of the hongge deposit is similar to that of some of the most primitive high ti basalts in the emeishan large igneous province the ferrobasaltic parental magma and the ferropicritic primary magma of the hongge intrusion are similar in major and trace element composition to the ferropicritic ferrobasaltic magma in the pechenga belt kola peninsula russia depletion of incompatible trace elements in the oxide ores and associated rocks in the hongge intrusion as compared to the coeval high ti basalts suggest that not all the magma involved in the development of the hongge intrusion has been retained in the intrusion the occurrence of multiple fe ti oxide layers alternating with fe ti oxide bearing silicate layers within a single zone and the repetitive appearance of sulfides olivine and cr rich layers suggest that multiple pulses of magma were involved in the formation of the hongge intrusion and related fe ti v oxide deposit we propose that the middle zone of the hongge intrusion was a magma stepwise flow through system and that some of the liquid was lost to the peripheral lavas to form the basalt

geochemical fingerprints in topsoils of the volcanic brava island cape verde abstract topsoils developed on different lithologies of all the geological units of the volcanic brava island cape verde archipelago were studied by neutron activation analysis and mossbauer spectroscopy sampling was performed according to the recommendations of the igcp 259 international geochemical mapping significant chemical contents variations were found even within the same volcano stratigraphic unit inherited from the parent rock composition under the semi arid climate of the island the chemical heterogeneity of topsoils within the same geological unit particularly in the upper unit was evidenced by a multivariate statistical analysis some differences found can be related with the geographical location underlying basement high contents of mn co ga ba la ce nd sm eu tb ta w th and u were observed in soils related to carbonatites and phonolites ree and w can be used to trace outcrops of extrusive carbonatites in general iron is strongly oxidized occurring in the silicates structure as well as in hematite oxidized magnetite and maghemite the global iron oxidation degree the fraction of fe 3 in silicates and the fraction of nanosized oxides which are higher in topsoils of the older units may be an indicator of weathering degree as br and sb contents were also found to increase with weathering topsoils developed on extrusive carbonatites are clearly distinguished due to the absence of fe 2 in the silicate phases and the remarkable predominance of low oxidized magnetite

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

geochemistry petrogenesis and metallogenesis of the panzhihua gabbroic layered intrusion and associated fe ti v oxide deposits sichuan province sw china the panzhihua gabbroic layered intrusion is associated with the 260ma emeishan large igneous province in sw china this sill like body hosts a giant fe ti v oxide deposit with 1333 million ton ore reserves which makes china a major producer of these metals the intrusion has a marginal zone of fine grained hornblende bearing gabbro and olivine gabbro followed upward by lower middle and upper zones the lower and middle zones consist of layered melanogabbro and gabbro composed of cumulate clinopyroxene plagioclase and olivine these zones also contain magnetite layers the upper zone consists chiefly of leucogabbro composed of plagioclase and clinopyroxene with minor olivine most rocks in the body show variable scale rhythmic modal layering in which dark minerals primarily clinopyroxene dominate in the lower parts of each layer and lighter minerals primarily plagioclase dominate in the upper parts the oxide ores occur as layers and lenses within the gabbros and are concentrated in the lower parts of the intrusion ore textures and associated mineral assemblages indicate that the ore bodies formed by very late stage crystallization of v rich titanomagnetite from an immiscible oxide liquid in a fluidrich environment the rocks of the panzhihua intrusion become more evolved in chemistry upward and follow a tholeiitic differentiation trend with enrichment in fe ti and v they are enriched in light rare earth elements relative to heavy rare earth elements and exhibit positive nb ta and ti anomalies and negative zr and hf anomalies the silicate rocks and oxide ores of the panzhihua intrusion formed from highly evolved fe ti v rich ferrobasaltic or ferropicritic magmas the textures of the ores and the abundance of minor hydrous phases indicate that addition of fluids from upper crustal wall rocks induced the separation of the immiscible oxide melts from which the fe ti v oxide ore bodies in the lower part of the intrusion crystallized

variations of trace element concentration of magnetite and ilmenite from the taihe layered intrusion emeishan large igneous province sw china implications for magmatic fractionation and origin of fe ti v oxide ore deposits abstract in situ la icp ms trace elemental analysis has been applied to magnetite and ilmenite of the taihe layered intrusion emeishan large igneous province sw china in order to understand better fractionation processes of magma and origin of fe ti v oxide ore deposits the periodic reversals in mg ti mn in magnetite and mg sc in ilmenite are found in the middle zone of the intrusion and agree with fractionation trends as recorded by olivine fo plagioclase an and clinopyroxene mg compositions these suggest the taihe intrusion formed from open magma chamber processes in a magma conduit with multiple replenishments of more primitive magmas the v and cr of magnetite are well correlated with v and cr of clinopyroxene indicating that they became liquidus phases almost simultaneously at an early stage of magma evolution ilmenite from the middle and upper zones shows variable cr ni v mg nb ta and sc contents indicating that ilmenite at some stratigraphic levels crystallized slightly earlier than magnetite and clinopyroxene the early crystallization of magnetite and ilmenite is the result of the high feot and tio2 contents in the parental magma the ilmenite crystallization before magnetite in the middle and upper zones can be attributed to higher tio2 content of the magma due to the remelting of pre existing ilmenite in a middle level magma chamber compared to the coeval high ti basalts the relatively low zr hf nb and ta contents in both magnetite and ilmenite throughout the taihe intrusion indicate that they crystallized from fe ti p rich silicate magmas positive correlations of ti with mg mn sc and zr of magnetite and zr with sc hf and nb of ilmenite also suggest that magnetite and ilmenite crystallized continuously from the homogeneous silicate magma rather than an immiscible fe rich melt therefore frequent replenishments of fe ti p rich silicate magma and gravitational sorting and settling are crucial for the formation the massive and apatite rich disseminated ores in the lower and middle zones of the taihe intrusion

integration of outcrop and borehole image logs for high resolution facies interpretation example from a fluvial fan in the ebro basin spain electrical borehole image logs yield high resolution information about variations in micro resistivity along the borehole wall to interpret these variations in terms of sedimentary structures and lithofacies types calibration with real rock is needed normally the only real rock available is core and this only provides one dimensional information in this paper the interpretation of fluvial facies types from borehole image logs was established by direct comparison with outcrops four fluvial facies associations were established in an outcrop study of a low net to gross fluvial succession i meandering rivers ii braided rivers iii crevasse deltas and iv crevasse splays the lithofacies characteristics and palaeocurrent distributions of each fluvial facies association were established two 200 m deep wells were drilled behind the cliff face outcrops one well was cored to a depth of 150 m and borehole image logs were recorded in both wells the wells were correlated with the outcrop the borehole image logs were analysed by their vertical colour succession and the dipmeter pattern image log facies were established and these were interpreted in terms of the fluvial facies associations encountered in the corresponding outcrops the study of borehole image logs yields a set of diagnostic criteria for a detailed fluvial facies interpretation and the establishment of depositional trends and thus provides a powerful tool for the direct interpretation of fluvial facies in a reservoir setting

on the origin of crevasse splay amalgamation in the huesca fluvial fan ebro basin spain implications for connectivity in low net to gross fluvial deposits abstract floodplain deposits are abundant in low gradient dryland river systems but their contribution to connected reservoir volumes has not yet been fully acknowledged due to their poor detectability with typical wireline log suites and relatively lower reservoir quality this study presents an analysis of stacked crevasse splays in the distal part of the miocene huesca fluvial fan ebro basin spain vertical stacking of crevasse splays implies local aggradation of the active channel belt lateral amalgamation of crevasse splays created an elevated rim around their feeder channel raising its bankfull height subsequent crevasse splays were deposited on top of their predecessors creating sand on sand contact through incision and further raising the active channel belt this process of channel belt super elevation repeated until an upstream avulsion occurred amalgamated crevasse splays constitute connected reservoir volumes up to 107 m3 despite their lower reservoir quality they effectively connect channel deposits in low net to gross fluvial stratigraphy and hence their contribution to producible volumes should be considered unswept intervals of amalgamated crevasse splays may constitute a secondary source of natural gas their interval thickness can serve as a proxy for feeder channel dimensions which can in turn be used to estimate the degree of stratigraphic connectivity

geochemistry and petrogenesis of the permian mafic dykes in the panxi region sw china abstract numerous intrusive bodies of ultramafic mafic to felsic compositions are exposed in association with volcanic rocks in the emeishan large igneous province lip southwestern china in this paper we present new elemental and isotopic data for the permian mafic dykes from the panxi region which is located in the western part of the emeishan lip the characteristics of major and trace elements and sr nd isotopes in combination with isotopic ages suggest that these mafic dykes were originated from a similar mantle source related to an upwelling mantle plume and their formation was involved in a process of variable degrees of fractional crystallisation coupled with assimilation of enriched crustal materials the mafic dyke samples from the panxi region show some systematic variations in geochemical compositions the gabbros in yanyuan contain the lowest ree e g la 5 12 ppm the highest mgo 8 38 21 33 and compatible elements e g cr 104 2610 ppm ni 135 496 ppm and display depleted sr nd isotopic ratios initial 87sr 86sr 0 703752 0 703844 end t 4 87 to 5 13 these gabbros likely represent an undifferentiated composition similar to primary melts derived from a depleted mantle source in contrast the gabbro samples from panzhihua and huili have more enriched lree abundances and incompatible elements and display depleted to slightly enriched sr and nd isotopic signatures initial 87sr 86sr 0 704354 0 705436 end t 0 29 to 4 58 though their trace element spidergram patterns are similar to those of the yanyuan samples these gabbros were formed probably through the removal of a few percent of olivine clinopyroxene plagioclase and apatite from the melts that formed the yanyuan gabbros all the mafic intrusives in the region exhibit elemental and sr nd isotopic features generally comparable with those of the nearby volcanic rocks in addition their emplacement immediately preceded or was synchronous with the main pulse of volcanism that formed lavas over a large area along the western margin of the yangtze craton these lines of evidence suggest that there is a genetic link between the mafic dykes and flood basalts in the emeishan lip and the both share a common mantle source related to the emeishan plume

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

platinum group element geochemistry of the layered intrusions in the emeishan large igneous province sw china implications for the principal controls on magmatic sulfide immiscibility it is widely accepted that the incorporation of external sulfur via crustal contamination is an important trigger for sulfide immiscibility that generates ni cu pge sulfide mineralization yet other controlling factors for sulfide immiscibility may also be present the late permian panzhihua baima hongge xinjie and taihe layered intrusions in the emeishan large igneous province elip sw china are well endowed with fe ti oxide deposits whereas their sulfide mineralization is mainly sub economic for example the lower part of the xinjie intrusion hosts a few thin pge rich ore layers yet other elip layered intrusions do not contain any ni cu sulfide mineralization and are pge depleted 0 01 1 ppb compared with the pge undepleted emeishan high ti basalts that are genetically related to the intrusions the extent of pge depletion and elevated cu pd ratios up to 3 2 106 of the panzhihua baima taihe and hongge intrusions suggest pge depletion in their parental magmas due to early stage sulfide removal sr nd isotopic compositions of the panzhihua baima and taihe intrusions suggest crustal contamination was insignificant and sulfide saturation produced mainly by crustal sulfur input was unlikely melts modeling shows that extensive fractionation of chromite olivine and clinopyroxene in deep seated magma chambers may have induced early stage sulfide saturation of the primary magmas the relatively high sulfide contents in the fe ti oxide layers at panzhihua baima hongge and taihe indicate a close relationship between the second stage sulfide immiscibility and extensive fe ti oxide crystallization positive correlations between sulfur and total fe2o3 v and tio2 suggest that fe ti oxide magnetite and ilmenite crystallization may have triggered the second stage sulfide saturation via sharply lowering the fe concentration and oxygen fugacity of the magmas moderate degree of crustal contamination for the xinjie fe ti oxide barren rocks may have induced sulfide saturation and accumulation at the lower part of the intrusion our calculations indicate that the xinjie pge rich rocks have high r factors 1000 10000 which are ascribed to pge upgrading of the sulfides via reaction with new replenishments of pge undepleted magmas a few panzhihua baima and taihe samples that contain higher pge concentrations suggest that the early stage sulfide droplets at depths were entrained in later magma pulses delivered to shallower magma chambers the very high r factors determined by mass balance calculation implies a good potential for discovering more pge mineralization in the deep seated intrusions of the magma plumbing system

rare earth and other trace and major elemental distribution in a pedogenic calcrete profile slimene ne tunisia a calcrete profile developed on the top of a calcareous consolidated dune located in a coastal area of ne tunisia semi arid climate was studied with the aim to investigate the behavior of the chemical elements rare earth elements ree and other trace and major elements during the processes associated with calcrete formation particularly dissolution and precipitation of carbonates in the vadose zone the profile shows a vertical sequence with clear zonations from the surface downwards a reddish soil at the land surface a nodular horizon a laminar structured level and the consolidated old dune chemical and mineralogical analyses of samples from all levels were performed by neutron activation analysis and x ray diffraction bulk samples and 2 m fraction detailed studies of iron speciation and iron minerals were done by mossbauer spectroscopy microfauna mineralogical and chemical variations in the slimene weathering profile point to a long term aerial exposure of the old dune in a semi arid carbonated environment leading to the development of a pedogenic calcrete profile the mineralogical variations with depth indicate carbonate dissolution at the surface and downward leaching of calcium secondary carbonates overgrow primary ones and precipitate as coating or concretions below minerals found in the upper levels correspond to original materials of the old dune and also weathering phases and atmospheric inputs phyllosilicates decrease while calcite and k feldspars increase with depth kaolinite was the only clay mineral found in the old dune illite and chlorite were also found in all samples with calcrete authigenic smectite formation occurs above the laminar structured calcrete due to restricted drainage conditions the most significant chemical variations associated with the calcrete formation are i enrichment of co u br and ree in calcrete ii depletion of middle ree in the upper levels particularly eu and enrichment of middle ree and heavy ree in calcrete and iii hf zr cr th cs ta ga rb and k appear to be retained in the upper levels where calcite has been dissolved here iron is more reduced fe3 occurs in iron oxides goethite and hematite and clay minerals the ratio goethite hematite appears to increase down the profile and fe2 is mainly present in clay minerals

chemical and mineralogical characterization of historic mortars from the santa eulalia de boveda temple nw spain bulk samples of mortars from the santa eulalia de boveda temple nw spain have been characterized from a chemical and mineralogical point of view with the aims of contributing technological and provenance inferences and evaluating possible correlations with the various identified stages along historical periods of construction mortar samples were analyzed by x ray diffraction and neutron activation analysis mineralogical associations found are similar quartz alkali feldspars calcite and mica for all samples only varying in their proportions mainly calcite statistical and geochemical studies allowed the differentiation of two main groups enhancing definition of the granite nature of the aggregate and of a significant variation in calcite proportion lime binder two outlying samples were identified one with higher calcite proportion and other corresponded to a plaster with a different raw material source a clear correlation between the chemical groups and the independently defined chronological stages could not be found in this work however mortar samples from the earlier stage were associated with a higher aggregate binder proportion

late oligocene early miocene paleosols of distal fluvial systems ebro basin spain abstract the study of paleosols can be a vital tool in the paleoenvironmental interpretation of continental deposits because their physical and chemical characteristics are a reflection of variations in aspects of soil formation changes in paleosol characteristics can be used to determine the architecture and nature of parent material paleosol maturity topography climate and soil forming organisms including vegetation cover on the ancient floodplain and can be utilized to recreate a palaeocatena furthermore paleosols can provide quantitative data on paleoclimate where other sources such as organic matter and pedogenic carbonate are absent late oligocene early miocene strata exposed in the ebro basin spain have been identified as proximal alluvial fan fluvial and lacustrine continental facies in parts of the distal fluvial system pedogenically altered channel and overbank deposits interfinger with ephemeral lacustrine facies three main paleosol types developed in these sediments and have been described and compared to modern soils entisol like early successional soils inceptisol like young soils and alfisol like open woodland soils paleoenvironmental reconstructions suggest a mosaic of ecotypes with areas of open woodland composed of shrubs herbs and small trees and other plants of low stature and with each ecotype being controlled primarily by fluctuating paleohydrological conditions from field observations and geochemical analysis the climate was found to be humid continental mean annual temperature mat 10 14 c 4 c mean annual precipitation map 450 830 mm yr 1 200 mm yr 1 these results indicate that climatic conditions were wetter than the present day ebro basin mat 14 c map 320 mm yr 1 and differ from previous interpretations of an arid to semi arid environment based on sedimentological criteria alone

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

petrogenesis of the pt pd mineralized jinbaoshan ultramafic intrusion in the permian emeishan large igneous province sw china the jinbaoshan ultramafic intrusion is a sheet like body with a thick wehrlite unit in the center and thin pyroxenite units at the margins pge are enriched in several disseminated sulfide zones in the intrusion olivine from the intrusion has low fo and depleted ni contents compared to olivine from coeval emeishan picrites whole rock major and trace element concentrations suggest that the jinbaoshan wehrlites originally contained 30 trapped liquid the total amount of sulfide in the rocks exceeds that which could have been dissolved in the trapped liquid the jinbaoshan wehrlites are interpreted to represent residual assemblages formed by dissolution of plagioclase by passing magma no clear evidence of crustal contamination is indicated by s nd and os isotopes we envision that sulfide saturation occurred at depth due to olivine and chromite crystallization immiscible sulfide droplets were transported to the jinbaoshan conduit where they accumulated and reacted with magma successively passing through the conduit to achieve high pge concentrations

a hierarchical approach for evaluating fluvial systems architectural analysis and sequential evolution of the high net sand content middle wasatch formation uinta basin utah well exposed three dimensional fluvial outcrops of the high net sand content middle wasatch formation in three canyon uinta basin utah were used to create and develop a new methodology for describing the architecture of fluvial systems the methodology builds on the works of campbell jackson allen and miall and addresses sedimentary processes scale and temporal context for reservoir and non reservoir bodies the methodology developed herein is a three level hierarchical framework that classifies meso and macroscale architecture of fluvial systems the three level hierarchy contains from smallest to largest stories elements and archetypes eight story types provide the foundational building blocks of this framework and account for sedimentation in both channel belt and floodplain belt elements including 1 downstream accreting 2 laterally accreting 3 erosionally based fine grained fill 4 fine grained fill associated with laterally accreting 5 levee 6 splay 7 crevasse or overbank channels and 8 floodplain fines two types of elements are recognized 1 channel belt and 2 floodplain belt an archetype consists of a channel belt element and its genetically related floodplain belt elements two distinct upward stacking patterns differentiate braided and meandering archetypes in deconstructing the evolution of archetypes three distinct associations between channel belt elements and their adjacent splays are documented 1 unassociated splays 2 associated coeval splays and 3 associated non coeval splays width and thickness for stories channel belt elements and archetypes are documented providing dimensional constraints for analog high net sand content fluvial systems additionally this methodology provides object based models with shape defined reservoir and nonreservoir geobodies that realistically compare to fluvial systems

temporal and spatial variations in magnetic properties of suspended particular matter in the yangtze river drainage and their implications abstract as the largest river of china the yangtze river transports large amounts of sediments to the adjacent oceans provenance of these ancient marine sediments can only be deciphered when the source to sink process of modern sediments in the yangtze river is fully understood many methods have been used to study the provenance of river sediment and an environmental magnetic method is applied in this study because of its fast nondestructive advantages magnetic properties of suspended particulate matter spm along the yangtze river were measured to provide a holistic understanding about magnetic properties of sediments in this river and its controlling factors the results indicate that the dominant magnetic mineral in spm is magnetite with a small contribution of hematite and goethite significant spatial variation was observed in most of the magnetic parameters which primarily reflects the distribution of major geologic units along the drainage area of the river anthropogenic influences are also recorded in the magnetic parameters the three gorges dam results in a dramatic decrease of magnetic minerals in the downstream reaches since its construction in 2003 in addition small variations in magnetic properties of spm are found along water depth together with a clear seasonal shift at datong station this seasonal variation of magnetic properties of spm is driven by variability in both hydrology and source contributions this complicates the use of magnetic parameters for provenance studies magnetic properties of sediments in rivers are capable of tracing provenance areas but caution must be taken into account

trace element geochemistry in topsoil from east china the concentrations of 23 trace elements in 50 topsoil samples collected from sites ranging between 18 19 n and 49 13 n in east china were analyzed sc ti v cr mn co ni cu zn ga and ta have mean contents more than two times higher than in the continental upper crust three elements rb sr and ba are present at lower concentrations than in the continental upper crust finally a group of elements consisting of ge y zr nb sc hf pb th and u are present at concentrations 1 2 times higher than in the continental upper crust however concentrations of trace elements are mainly affected by parent rock the contents of sc ti v cr mn co and cu for 29 soils from basalt were found to increase from north to south whereas rb sr and ba contents were found to decrease in addition element concentration shows a close relationship with annual average temperature aat as well as annual average precipitation aap since the 29 soils are all from basalt the trends of the elemental contents should reflect the influence of climate which determines the intensity of weathering these elemental trends suggest that the content of certain elements may indicate the intensity of basalt weathering ba nb and sr nb ratios were both found to have good correlations with aat and aap in this study which means that these ratios can also indicate the intensity of chemical weathering of basalt

multiple magma evolution and ore forming processes of the hongge layered intrusion sw china insights from sr nd isotopes trace elements and platinum group elements abstract the hongge layered intrusion 259 ma which is located in the inner zone of the emeishan large igneous province elip is one of the most typical fe ti v ore deposits in the pan xi area mafic ultramafic layered intrusions of the elip have attracted a lot of attention lately because these intrusions host world class fe ti v oxide deposits plus interesting cu ni pge mineralization which may have economic potential this paper reports new whole rock major and trace element compositions pge abundances and sr nd isotopic data for selected cumulate rocks and basalts we use these data to investigate the nature of parental magmas and the controls on its evolution from the source mantle en route to the surface involving the hongge ore bearing intrusion two abrupt changes in mt ilm and trace element ratios such as ba th with depths in the hongge layered intrusion indicate that this intrusion formed by at least two pluses of relatively primitive magma the whole rock sr nd isotopic data of basaltic and intrusive rocks plot in the region of emeishan low ti basalts and the compositions of residual liquid at 1260 c and 1155 c calculated by melts are similar to our actual high ti bfq 2 and low ti bc 1 basltic samples indicate they are co magmatic rather than derivation from a distinct source total pge abundances in the hongge samples are extremely low ranging from 0 5 to 10 ppb sulfide bearing rocks in the hongge intrusion and the nearby coeval banfangqing and baicao basalts have similar mantle like pd pt ratios 2 6 and extremely high cu pd ratios 3 104 to 4 105 indicating that sulfide segregation took place at depth prior to emplacement at hongge and eruption in this region sulfide saturation in the hongge magma may have resulted from such crustal contamination event crystallization of silicate minerals under the anhydrous magma magma hydration plus fe ti enrichments in the parental magma are three critical factors for the formation of fe ti oxide ore layers in the hongge intrusion

splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia abstract splays are common features of many rivers and deltas forming as a result of overbank flooding and sediment deposition but they have rarely been described from modern dryland settings this paper investigates splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia here splays vary from small lobate or tongue shaped features 1 km long to larger elongate features up to 4 km long and are supplied with rare floodwater and sediment through well defined breaches in the upper parts of the main channel banks in proximal and medial parts splay channels are incised up to 2 m into pre splay fine grained floodplain sediments but remain elevated between 0 5 m and 2 m above the main channels only in the very distal parts are splay channels less deeply incised either grading into the floodplain surface or terminating as sediment lobes that are deposited upon the floodplain aerial photographs and field observations indicate that many splays develop rapidly during large floods and are modified during infrequent subsequent floods four main stages of splay development are proposed 1 aggressive overbank flow results in bank line breaching and channel scour on the floodplain but little sediment deposition 2 coarse bed sediment is diverted from the main channel preventing further deepening at the bank line breach and slowing channel scour 3 increasing coarse sediment transport through the bank line breach and scoured channels leads to the formation of distal sediment lobes 4 subsequent floods divert around these distal lobes sometimes leading to further channel scour and lobe formation on the northern plains splays contribute to downstream decreases in the discharge and size of the main channels and splay deposits form local accumulations of gravelly sand in the predominantly fine grained floodplain successions some splays ultimately may evolve into distributaries or anabranches the dominantly erosional bases of these splay channels contrast with typical descriptions of many humid region splays but they do not display any geomorphological or sedimentological features that are necessarily diagnostic of formation in a dryland setting

integrated o sr nd isotope constraints on the evolution of four important fe ti oxide ore bearing mafic ultramafic intrusions in the emeishan large igneous province sw china abstract in the emeishan large igneous province sw china there are many layered mafic ultramafic intrusions such as the baima hongge panzhihua and taihe intrusions that host world class fe ti oxide ore deposits despite numerous studies the origin of these deposits still remains elusive this includes the role of crustal contamination especially addition of external co2 from carbonate country rocks during contact metamorphism in triggering fe ti oxide crystallization from high mg basaltic magma to address this important issue we have carried out an integrated o sr nd isotope study of these ore bearing intrusions and the country rocks our results show that in these intrusions clinopyroxene is much less susceptible to fluid mineral oxygen isotope exchange than coexisting plagioclase and fe ti oxides which is similar to other intrusions worldwide e g taylor 1967 gregory and taylor 1981 our calculations based on the least exchanged clinopyroxene oxygen isotope data show that the mean 18o values for the parental magmas of these intrusions are baima 5 7 panzhihua 6 1 taihe 5 9 the estimated mean 18o value for the parental magma of the upper and middle zones of the hongge intrusion is 6 2 which is similar to those for the parental magmas of the other intrusions baima panzhihua and taihe by contrast the estimated mean 18o value for the parental magma of the lower zone of the hongge intrusion is higher 6 9 this difference together with higher initial 87sr 86sr ratios 0 7057 to 0 7076 and lower endt values 2 82 to 0 07 for this zone can be attributed to higher degrees of contamination with siliceous crustal materials in this zone than elsewhere in this intrusion comparison of o sr nd isotope compositions between the intrusions and country rocks reveals that bulk assimilation of carbonate country rocks is negligible in all of these intrusions mixing calculations using the o sr nd isotope data are consistent with variable degrees of contamination with siliceous crustal materials in the intrusions panzhihua

three fe ti oxide ore bearing gabbro granitoid complexes in the panxi region of the permian emeishan large igneous province sw china the permian 260 ma emeishan large igneous province of sw china contains three nearly identical gabbro granitoid complexes that host giant fe ti oxide deposits the fe ti oxide deposits are within the lower portions of evolved layered gabbroic intrusions and are spatially and temporally associated with a type granitic plutons the 264 3 ma taihe layered gabbroic intrusion hosts a large magmatic fe ti oxide deposit and is coeval with the taihe peralkaline a type granitic pluton which is dated at 261 2 ma within the a type granitic pluton are microgranular enclaves which have compositions intermediate between the gabbro and host granite primitive mantle normalized incompatible element plots show corresponding reciprocal patterns between the mafic and felsic rocks the chondrite normalized ree patterns show eu anomalies changing from positive eu eu 1 5 to 5 9 in the gabbroic intrusion to negative in the enclaves eu eu 0 4 to 0 6 and granites eu eu 0 2 to 0 5 whole rock end t values of the gabbroic intrusion end t 2 5 to 3 3 are similar to those of the enclaves end t 1 0 to 2 0 and granite end t 1 5 to 1 9 whereas the zircon ehf t values of the gabbro ehf t 8 1 0 8 are indistinguishable from those of the granites ehf t 9 2 1 0 suggesting that the parent magmas for all rock types originated from the same mantle source geochemical modeling indicates that the gabbros and granites can be generated by fractional crystallization of a common parental magma similar to high ti emeishan flood basalt the compositional jump from the gabbro to the enclaves is attributed to the crystallization of fe ti oxide minerals the results of this study and other studies suggest that the magmatic conditions for example pressure composition fo2 which led to the formation of at least three fe ti oxide bearing gabbro granitoid complexes were relatively common during the development of the emeishan large igneous province

rhenium osmium isotope and platinum group elements in the xinjie layered intrusion sw china implications for source mantle composition mantle evolution pge fractionation and mineralization abstract the xinjie mafic ultramafic layered intrusion in the emeishan large igneous province elip hosts cu ni platinum group element pge sulfide ore layers within the lower part and fe ti v oxide bearing horizons within the middle part the major magmatic cu ni pge sulfide ores and spatially associated cumulate rocks are examined for their pge contents and re os isotopic systematics the samples yielded a re os isochron with an age of 262 27 ma and an initial 187 os 188 os of 0 12460 0 00011 os t 0 5 0 1 the age is in good agreement with the previously reported u pb zircon age indicating that the re os system remained closed for most samples since the intrusion emplacement they have near chondritic os t values ranging from 0 7 to 0 2 similar to those of the lijiang picrites and song da komatiites exceptionally two samples from the roof zone and one from upper sequence exhibit radiogenic os t values 0 6 to 8 6 showing minor contamination by the overlying emeishan basalts the pge rich ores contain relatively high pge and small amounts of sulfides generally less than 2 and the abundance of cu and pge correlate well with s implying that the distribution of these elements is controlled by the segregation and accumulation of a sulfide liquid some ore samples are poor in s mostly t and cr tio 2 ratios immediately below units 2 4 together with high cu zr ratios decreasing from each pge ore layer within these cyclic units are consistent with multiple magma replenishment episodes the sulfides in the cumulate rocks show little evidence of pge depletion with height and thus appear to have segregated from successive inputs of fertile magma this suggests that the xinjie intrusion crystallized from in an open magma system e g a magma conduit the compositions of the disseminated sulfides in most samples can be modeled by applying an r factor silicate sulfide mass ratio of between 1000 and 8000 indicating the segregation of only small amounts of sulfide liquid in the parental ferropicritic magmas thus continuous mixing between primitive ferropicritic magma and differentiated resident magma could lead to crystallization of chromite cr bearing magnetite and subsequently abundant fe ti oxides thereby the segregation of pge rich cu sulfide when considered in the light of previous studies on plume derived komatiites and picrites worldwide the close to chondritic os isotopic composition for most xinjie samples lijiang picrites and song da komatiites suggest that the ferropicritic magma in the elip were generated from a plume this comprised recycled neoproterozic oceanic lithosphere including depleted peridotite mantle embedded with geochemically enriched domains the ascending magmas thereafter interacted with minor possibly

crevasse splay morphodynamics in a dryland river terminus rio colorado in salar de uyuni bolivia high resolution satellite imagery in combination with field investigation enables the analysis of splay morphological developments in time and space at the low gradient terminus of the modern rio colorado dryland river system in the salar de uyuni bolivia two sets 2004 2005 2010 2011 of satellite images are used to visualize splay morphological developments and three types of crevasse splays are identified based on temporal changes 1 new crevasse splays ncs refers to those splays that are not observed in the first set of images but can be observed on the second sets of images 2 changing crevasse splays ccs representing those splays that are found on the first set of images but their geometry has changed between two satellite observation periods and 3 inactive crevasse splays ics referred to those splays that are found on the first set of images but on the second set of images they remain the same or are partially overlapped by adjacent expanding crevasse splays the density or frequency of these three types of crevasse splays has no correlation with the distance to the starting point of the river or the local slope the cross sectional area of the studied river steadily decreases downstream and frequency analysis shows a downstream increase in the number of crevasse splays and suggests an exponential relationship with the river cross sectional area development of crevasse splays is often attributed to topographic lows between adjacent crevasse splays and they fill in the depression by compensational stacking e g li et al 2014 these amalgamated splays are capable of forming a large area of sheet sands and potentially provide an analogue for thin bedded hydrocarbon reservoirs

permian peralkaline peraluminous and metaluminous a type granites in the panxi district sw china their relationship to the emeishan mantle plume abstract numerous permian granitic intrusions plutons in the panxi region sw china are spatially and temporally associated with the emeishan large igneous province elip granites from the 260 ma panzhihua and taihe plutons are peralkaline asi 0 76 1 12 na k al 0 78 1 2 and have high fe values 0 92 0 99 with negative eu anomalies eu eu 0 22 0 98 contrasted with the peralkaline plutons syenites from the 260 ma woshui pluton are metaluminous asi 0 84 1 0 na k al 0 91 1 01 and have moderately high fe 0 79 0 81 and positive eu anomalies eu eu 0 82 1 91 both the peralkaline and metaluminous rocks have mantle isotopic signatures end t 1 3 3 2 and were derived from the elip mantle plume source the peralkaline rocks were likely derived by fractional crystallization of the temporally spatially and chemically associated layered mafic intrusions which host giant magmatic fe ti v oxide deposits the metaluminous granitic rocks although spatially related to the peralkaline granites and layered gabbros were likely generated by partial melting of underplated mafic rocks granites from the 251 ma ailanghe pluton are peraluminous asi 0 97 1 29 and have high fe 0 82 0 91 values and negative eu anomalies eu eu 0 10 0 37 their crustal isotopic signature end t 5 7 to 6 7 indicates possible derivation from melting of yangtze block basement rocks the ailanghe pluton is contemporaneous with other a type granites in the region supporting the view that elip magmatism was sporadic for at least 9 million years the coexistence of three chemically exclusive a type granites in the elip suggests that a variety of a type granites can be generated in the same tectonic setting

the formation of p rich fe ti oxide ore layers in the taihe layered intrusion sw china implications for magma plumbing system process abstract the taihe intrusion is one of the layered intrusions that host giant fe ti oxide deposit in the central part of the emeishan large igneous province sw china different from the other layered intrusions the taihe intrusion has a massive fe ti oxide ore layer at the top of the lower zone lz particularly the rocks of both middle and upper zones contain as much as 5 12 apatite and the most important fe ti oxide ore layers apatite magnetite clinopyroxenite occur at the bases of cyclic units in the middle zone mz rather than in the lower zone lz high cr and ni concentrations of clinopyroxene 65 263 ppm and 66 83 ppm respectively and high an contents of plagioclase 79 80 of the lz rocks indicate their more primitive parental magmas the clinopyroxene and plagioclase of the mz rocks are characterized by low cr and ni contents 1 21 ppm and 0 4 10 ppm respectively and low an 51 67 indicating more evolved parental magma the fe ti oxide ore layers in the mz are not only high in fe and ti but also enriched in p2o5 and rare earth elements indicating an unusual fe ti p rich parental magma it is speculated that the mz represents a later intrusion of fe ti p rich magmas that were produced by the fe ti enriched magma from a deep seated magma chamber mixing with the extensively evolved p rich magma in a middle level magma chamber early crystallization and cumulation of fe ti oxide and apatite together with clinopyroxene from the fe ti p rich magmas from the middle level magma chamber resulted in the formation of fe ti oxide ore layers in the mz fe ti p rich magma and apatite magnetite clinopyroxenites occur in the base of cyclic units whereas apatite gabbros are presented at the upper parts of each cyclic unit the upper zone uz is the product of the crystallization of highly differentiated magma consists chiefly of apatite gabbro and minor intercalated apatite clinopyroxenite

mineral characteristics and metallogenesis of the wajilitag layered mafic ultramafic intrusion and associated fe ti v oxide deposit in the tarim large igneous province northwest china abstract the wajilitag layered mafic ultramafic intrusion as an important lithological unit of the permian tarim large igneous province has genetic link with a large scale v bearing ilmenite titanomagnetite series mineralization it consists mainly of olivine pyroxenite pyroxenite and gabbro with layered structures olivine from the mafic ultramafic rocks has low fo values molar 100 mg mg fe of 67 76 mol probably indicating that the wajilitag magmas have experienced fractional crystallization with an early removal of olivine magmas in equilibrium with olivine have high feo mgo ratios ranging of 1 1 1 6 ilmenite exsolution lamellae are present in clinopyroxene the wajilitag magmas therefore are considered to be enriched in iron and titanium which may account for the large amounts of fe ti oxides hosted therein high sm yb ratios indicate that the fe ti rich wajilitag magmas may be produced by low degree of partial melting from the mantle source layered structures and variable mineral compositions of olivine and clinopyroxene of the intrusion suggest that the magmas become more fe ti rich under extensively fractional crystallization from the evolved magma a few fe ti oxide crystals enclosed in the olivine of the olivine pyroxenite with slightly higher cr2o3 contents than other oxides indicate that minor oxides crystallized in the early stage of the magmatic process whereas most oxides interstitial to the silicate minerals denote that they were accumulated in the late stage of the magmatic process we propose that the fe ti oxides of the wajilitag intrusion were formed by fractionation processes with two stages the presence of ilmenite exsolution lamellae in magnetite suggests that the wajilitag layered mafic ultramafic intrusion and the massive fe ti ore deposits hosted therein formed in a slowly cooling magmatic crystallization process from a deep magma chamber

controls on the metal compositions of magmatic sulfide deposits in the emeishan large igneous province sw china abstract magmatic sulfide deposits in the emeishan large igneous province sw china have variable chalcophile and siderophile metal contents and can be divided into pge ni cu pge and ni cu deposits pge sulfide deposits include the jinbaoshan and zhubu deposits and have ores with very low sulfide contents 1 to 2 vol and very high pt and pd 0 3 to 10 ppm and ir 0 02 to 0 5 ppm typical ni cu pge sulfide deposits include the yangliuping and qingkuangshan deposits which contain sulfide ores with more than 10 vol sulfides 0 1 6 2 wt ni 0 03 11 wt cu and have moderate pge contents 0 1 5 ppm pt 0 01 1 8 ppm pd on the 100 sulfide basis pt and pd correlate positively with ir in the ores from the pge deposits whereas they correlate negatively in the ni cu pge and ni cu deposits pge geochemistry and model calculations indicate that the pge rich sulfides were separated from primary basaltic magmas whereas the ni cu pge sulfides were produced from magmas that had experienced minor sulfide removal about 0 01 and the ni cu sulfides were separated from magmas that experienced about 0 025 sulfide segregation fractionation of monosulfide solid solution resulted in differentiation between ipge and ppge in the ni cu pge and ni cu deposits

neoproterozoic bimodal magmatism in the cathaysia block of south china and its tectonic significance shrimp u pb zircon age geochemical and sm nd isotopic results are reported for the mamianshan volcanic rocks in the cathaysia block of southeastern south china the mamianshan volcanic rocks are bimodal in composition and are dominantly transitional to mildly alkaline basalts and subordinate alkaline rhyolite with an eruption age of 818 9 ma the basaltic samples are characterized by lree enriched and humped trace element patterns similar to many alkali basalts in continental rifts variablend t values between 3 33 and 4 35 indicate that the primary magma of these basalts was derived from an oib like mantle source and underwent fractional crystallization plus crustal contamination the rhyolitic rocks are highly enriched in th ta nb ree zr hf and y and depleted in sr p eu and ti sharing affinity to a 1 type granites combined with their slightly positive nd t values 0 22 to 0 92 the mamianshan felsic rocks were most likely generated by partial melting of the regional paleoproterozoic mayuan amphibolites the mamianshan bimodal volcanic rocks in the cathaysia block are coeval with the widespread intraplate magmatism around the yangtze block our results support the idea that a coherent south china craton was formed during the ca 1 0 ga sibao orogeny and it subsequently underwent extensive continental rifting related to mantle plume or superplume activities beneath rodinia since ca 825 ma 2004 elsevier b v all rights reserved

landsat imagery based visualization of the geomorphological development at the terminus of a dryland river system abstract in this remote sensing based study we present the analysis of the geomorphological development at the low gradient terminus of the modern rio colorado dryland river system in the endorheic altiplano basin bolivia changes in the river morphology occur after short periods of catastrophic peak discharge which result in the expansion of existing crevasse splays formation of new crevasse splays and in river path avulsion episodic peak discharge events in the study area were pinpointed and quantified by combining daily precipitation records from gauging stations in the vicinity with catchment area analysis from aster global dem gdem remote sensing data a time series of landsat imagery for the period 1975 2001 was then used to analyze the river morphology changes after major peak discharge events compensational stacking of crevasse splays in combination with river avulsion produced a thin but aerially extensive connected sand sheet at the terminus of the fluvial system

global geochemical mapping and its implementation in the asia pacific region abstract igcp projects 259 international geochemical mapping and 360 global geochemical baseline under the aegis of unesco s international geochemical correlation program made recommendations for standardizing geochemical mapping protocols and for conducting a wide spaced sampling of the earth s land surface based on a global reference network of approximately 5000 160 160 km cells a pilot study has been conducted throughout china during which these recommendations were implemented during the pilot study 500 floodplain samples representing drainage basins ranging in area from 1000 to 6000 km2 were collected throughout china and analyzed the widely spaced sampling used for the pilot study was compared to the very dense sampling million samplings of sediment for all of china used for china s regional geochemical national reconnaissance program the geochemical maps generated from the wide spaced sampling are strikingly similar to those generated from data based on the detailed sampling such low density floodplain sampling presents a relatively low cost way to get a quick overview of the geochemistry of a large area of the earth s surface the implementation of this project in the asia pacific region and the problems encountered are discussed in the present paper

geochemistry of the emeishan flood basalts at yangliuping sichuan sw china implications for sulfide segregation a well developed 1 000 m thick basaltic sequence in the yangliuping region northern part of the emeishan basalt province includes the lower and middle units of tholeiitic basalts and an upper unit of both tholeiites and subalkalic basalts the basalts contain 42 55 wt sio2 and 4 1 8 3 wt mgo most of these lavas have gd yb 2 0 zr nb 12 and nd 260 ma values from 2 5 to 4 7 the platinum group elements pge are very mildly depleted in most of the basalts which contain 8 19 ppb pt and 7 27 ppb pd however a significant proportion of the middle unit basalts are strongly depleted in pge with some samples having concentrations lower than detection limits they have extremely high zr nb ratios up to 14 5 and low nd 260 ma values 3 21 to 0 65 features of extensive lower crustal contamination some samples in this unit have high ni pd 3 965 61 198 and low pd cr 410 000 3 930 000 ratios indicating sulfide segregation and pge depletion prior to eruption the primary magmas were s undersaturated and derived from partial melting at variable depths in the upper mantle the early and late stage magmas as represented by the lower and upper units underwent afc processes which induced mild s saturation and pge depletion in some of the basalts whereas the magmas represented by the middle unit experienced more extensive crustal contamination resulting in stronger s saturation and in most cases significant pge depletion

chalcophile element geochemistry of the baima layered intrusion emeishan large igneous province sw china implications for sulfur saturation history and genetic relationship with high ti basalts the permian baima mafic layered intrusion believed to be related to the s undersaturated emeishan high ti basalts hosts a giant fe ti v oxide deposit in the lower part of the intrusion uniformly high cu pd 1 9 106 6 1 104 and low pd zr 0 1 indicate that the baima parental magma experienced prior sulfide segregation mantle liked 34s values and low s se values indicate negligible external sulfur addition primitive mantle normalized pge patterns and melts calculations indicate that extensive fractional crystallization 59 of chromite olivine and pyroxene at depth drove the primitive picritic magma to s saturation strong positive correlation between ipge and ppge and between pge and v cr and s suggest that magmatic sulfide is the dominant mineral controlling the distribution of pge in the baima intrusion a positive correlation between s and cr feot tio2 and v content together with melts calculations indicate that the parental magma of the baima intrusion reached a second stage of s saturation in the shallower baima magma chamber which was likely triggered by decreasing fe2 accompanying magnetite precipitation primitive mantle normalized pge patterns for baima intrusion rocks display similar trends to high ti basalts inside the panxi area suggesting that they are comagmatic and following a similar differentiation trend however the lavas erupted before they reached sulfide saturation the more evolved nature of high ti basalts outside the panxi area indicate that they experienced more extensive pre eruption fractional crystallization further fractional crystallization process led these lavas show more pge fractionated feature

characterizing avulsion stratigraphy in ancient alluvial deposits guidelines for identifying ancient avulsion deposits were set forth by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 building on the study by smith et al smith n d cross t a dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 23 of the modern saskatchewan river system cumberland marshes central canada and serve to characterize avulsion depositional sequences in the ancient willwood and fort union formations paleogene bighorn basin nw wyoming usa we recognize however that the model is not universally applicable to avulsion dominated successions specifically systems which lack defining heterolithic avulsion deposits set forth by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 observations in several fluvial intervals suggest that the avulsion stratigraphy outlined by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 represents one category of avulsion stratigraphy found in the rock record but does not capture the nature of avulsion deposits everywhere based on observations using measured sections outcrop photo panels and aerial photographs in the willwood formation eocene wyoming and ferris formation cretaceous paleogene wyoming we present two end member categories of avulsion stratigraphy in ancient deposits stratigraphically abrupt when a main paleochannel is stratigraphically juxtaposed directly atop floodplain overbank deposits and stratigraphically transitional where crevasse splays and other non floodplain overbank deposits stratigraphically precede a main paleochannel this characterization provides a broader more inclusive way to recognize and describe avulsion stratigraphy in ancient deposits and may be an important factor to consider when modeling connectivity in fluvial reservoirs furthermore our observations show that one type of avulsion channel stratigraphy may prevail over another within an ancient basin suggesting that system wide factors such as splay proneness or avulsion style i e aggradational incisional etc slingerland r smith n d 2004 river avulsions and their deposits annual review of earth and planetary sciences 32 257 285 may be primary controls on the type of avulsion stratigraphy deposited and preserved in ancient basin fills

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

petrography and trace element signatures in silicates and fe ti oxides from the lanjiahuoshan deposit panzhihua layered intrusion southwest china abstract permian mafic ultramafic layered intrusions in the central part of the emeishan large igneous province elip southwestern china host fe ti v oxide ores that have features which distinguish them from other large layered intrusion hosted deposits the origin of these ores is highly debated careful petrographic examination whole rock analysis electron probe microanalysis and measurement and mapping of trace element concentrations by laser ablation inductively coupled plasma mass spectrometry in all major and minor minerals clinopyroxene plagioclase olivine amphibole titanomagnetite ilmenite pleonaste and pyrrhotite has been undertaken on samples from the lanjiahuoshan deposit representing the middle lower and marginal zone of the panzhihua intrusion features are documented that impact on interpretation of intrusion petrology and with implications for genesis of the fe ti v oxide ores firstly there is evidence as symplectites between clinopyroxene and plagioclase for introduction of complex secondary melts secondly reaction between a late hydrothermal fluid and clinopyroxene is recognized which has led to formation of hydrated minerals pargasite phlogopite as well as a potassium metasomatic event postdating intrusion solidification which led to formation of k feldspar lastly partitioning of trace elements between titanomagnetite and silicates needs to consider scavenging of metals by ilmenite mn sc zr nb sn hf and ta and sulfides as well as the marked partitioning of co ni zn ga as and sb into spinels exsolved from titanomagnetite the role of these less abundant phases may have been understated in previous studies highlighting the importance of petrographic examination of complex silicate oxide sulfide assemblages as well as the need for a holistic approach to trace element analysis acknowledging all minerals within the assemblage

contrasting parental magma compositions for the hongge and panzhihua magmatic fe ti v oxide deposits emeishan large igneous province sw china many 260 ma mafic ultramafic layered intrusions including hongge and panzhihua in the emeishan large igneous province southwestern china host world class fe ti v oxide ore deposits these two most important ore bearing intrusions show differences in lithology and mineral chemistry the most important orebodies in the hongge intrusion occur as concordant layers in the middle part of the intrusion closely associated with clinopyroxenites titanomagnetite and mg rich ilmenite are the major ore minerals of the hongge deposit coexisting clinopyroxene contains 1 7 wt tio2 these data indicate high ti parental magma for the hongge ore bearing clinopyroxenites in the panzhihua intrusion the most important orebodies also occur as concordant layers but in its lower part instead of middle part in contrast with the hongge deposit the most important host rocks of the panzhihua deposit are gabbros not clinopyroxenites in addition ilmenite is rare and titanomagnetite is predominant in the panzhihua deposit coexisting clinopyroxene in the panzhihua deposit contains 1 6 wt tio2 the contrasting lithologic and mineral compositions indicate that the parental magma for the hongge deposit has higher tio2 than that for the panzhihua deposit the compositions of clinopyroxene from the panzhihua and hongge deposits indicate that their parental magmas are also different in mgo feo and trace element ratios as well calculations using average experimental mg fe exchange coefficient and trace element partition coefficients between clinopyroxene and magma show that the hongge parental magma has higher mgo feo ratios and more fractionated mantle normalized trace element patterns than the panzhihua parental magma the estimated compositions of the parental magmas for the hongge and panzhihua ore bearing lithologies resemble the average compositions of the longzhoushan type high ti basalts and ertan type intermediate ti basalts in the emeishan large igneous province respectively the new trace element data from this study together with available sr nd isotope data for the ore bearing intrusions from literature support a new petrogenetic model involving selective assimilation of newly subducted stagnant oceanic gabbroic slab above the deep seated emeishan mantle plume this process and subsequent contamination with the upper crust played an important role in the variation of parental magma compositions between the hongge and panzhihua magmatic oxide ore deposits abundant fe ti oxide ore deposits associated with less evolved basaltic magma in the emeishan large igneous province than elsewhere in the world are attributed to selective assimilation of newly subducted stagnant oceanic lithospheric slab by the ascending mantle plume derived picritic magma that was originally undersaturated with fe ti oxides