geochemical characteristics of fine and coarse fractions of sediments in the yarlung zangbo river basin southern tibet china tracing sources of aeolian sediment is key to reconstructing earth surface processes in arid areas and interpreting the paleoenvironmental significance of aeolian sequences however the difference of geochemical characteristics between different fractions of sediments in the yarlung zangbo river basin yzrb is still unclear so we want to identify which fraction of sediments is more suitable for tracing sediment sources considering the long distance between different wide valleys in the yzrb we wonder whether there is any difference between these wide valleys in terms of geochemical characteristics of sediments forty three surface sediment samples in the yzrb are collected and the grain size distributions and the major element composition for 37 samples and the trace and rare earth element composition for the coarse 75 500 m and fine 75 m fractions of all samples are determined the results reveal the following 1 the fine fractions of the deposits contain more environmental information suggesting that the fine fractions cannot be directly compared between different climate zones for provenance identification and that appropriate coarse fractions based on the grain size distribution of the targeted sediments are more ideal for tracing sediment sources and 2 geochemical characteristics of various sediment types show spatial heterogeneity the coarse and fine fractions of the loose sediment samples can be divided into two regional groups based on geochemical characteristics the maquanhe zone in the upper reach the xigaze shannan and mainling zone in the middle reach which is consistent with the geological background of the yzrb 3 aeolian deposits in the yzrb are a local origin and predominantly derived from the adjacent loose sediments and fluvial sediments in the upper reach contribute little to the aeolian sands in the middle reach

evidence suggesting that methods of rock varnish cation ratio dating are neither comparable nor consistently reliable abstract using samples from a prehistoric quarry site in the mojave desert we tested and compared the two principal methods of rock varnish cation ratio dating analysis of rock varnish scrapings r i dorn 1983 quaternary research 20 49 73 and 1989 physical geography 13 559 596 and analysis of rock varnish in situ c d harrington and j w whitney 1987 geology 15 967 970 because we found no consistent relationship between the varnish cation ratio k ca ti and the relative age of the varnish neither method could be used to cation ratio date the underlying chert artifacts moreover in situ analyses yielded systematically higher cation ratios and lower ti abundances than bulk analyses of scraped varnish or microprobe analyses of varnish in cross section our results when considered along with other recently published evidence indicate that these two methods of varnish chemical analysis and cation ratio dating may not be comparable nor consistently reliable chronometers

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

relative dating of terraces of the owens river northern owens valley california and correlation with moraines of the sierra nevada abstract in the northern owens valley the owens river has cut and preserved three terraces uplifted above its modern floodplain we have analyzed soils and used other relative dating techniques in order to differentiate the terrace surfaces to correlate from the terraces to moraines of the eastern sierra nevada and to test the effects of relief and climatic differences on relative dating results most of the relative dating techniques attempted were successful in differentiating the terraces of the owens river sequence in addition weathering rinds soil descriptions and an early holocene 14 c date for the youngest terrace support correlation of the three terrace levels with the three post sherwin age glacial stages tioga tahoe and pre tahoe found in nearby canyons of the sierra nevada other relative dating techniques that are commonly employed however suggest distinct differences between the terrace and moraine sequences these differences probably reflect the difference in relief such that slow erosion of the moraine crests may have retarded soil development relative to the flat terrace surfaces and altered surface weathering processes use of relative dating analyses to correlate between dissimilar geomorphic systems requires caution but use of a broad range of techniques and absolute age calibration may make correlation possible

hydrothermal venting and mineralization in the crater of kick em jenny submarine volcano grenada lesser antilles kick em jenny is a frequently erupting shallow submarine volcano located 7 5 km off the northern coast of grenada in the lesser antilles subduction zone focused and diffuse hydrothermal venting is taking place mainly within a small 70 110 m depression within the 300 m diameter crater of the volcano at depths of about 265 m much of the crater is blanketed with a layer of fine grained tephra that has undergone hydrothermal alteration clear fluids and gas are being discharged near the center of the depression from mound like vents at a maximum temperature of 180 c the gas consists of 93 96 co2 with trace amounts of methane and hydrogen gas flux measurements of individual bubble streams range from 10 to 100 kg of co2 per day diffuse venting with temperatures 5 35 c above ambient occurs throughout the depression and over large areas of the main crater these zones are colonized by reddish yellow bacteria with the production of fe oxyhydroxides as surface coatings fragile spires up to several meters in height and elongated mounds up to tens of centimeters thick a high resolution photomosaic of the inner crater depression shows fluid flow patterns descending the sides of the depression toward the crater floor we suggest that the negatively buoyant fluid flow is the result of phase separation of hydrothermal fluids at kick em jenny generating a dense saline component that does not rise despite its elevated temperature

submarine venting of magmatic volatiles in the eastern manus basin papua new guinea abstract the susu knolls and desmos hydrothermal fields are located in the back arc extensional transform zone of the eastern manus basin in 2006 highly acidic and so4 rich vent fluids were collected at both sites and analyzed for the chemical and isotopic composition of major and trace species fluids exiting the seafloor have measured temperatures from 48 to 215 c and are milky white in appearance due to precipitation of elemental s0 vent fluid concentrations of na k and mg are depleted by as much as 30 relative to seawater but have the same relative abundance in contrast the fluids are highly enriched in dissolved co2 cl sio2 aq fe and al relative to seawater measured ph 25 c ranged from 0 95 to 1 87 and aqueous so4 ranged from 35 to 135 mmol kg the chemical and isotopic composition points to formation via subsurface mixing of seawater with a na k mg and ca free volatile rich magmatic fluid exsolved from subsurface magma bodies during a process analogous to subaerial fumarole discharge estimates of the magmatic end member composition indicate a fluid phase where h2o so2 co2 cl f the hydrogen and oxygen isotopic composition of h2o and carbon isotopic composition of co2 in the vent fluids strongly suggest a contribution of slab derived h2o and co2 to melts generated in the mantle beneath the eastern manus volcanic zone abundant magmatically derived so2 undergoes disproportionation during cooling in upflow zones and contributes abundant acidity so42 and s0 to the venting fluids interaction of these highly acidic fluids with highly altered mineral assemblages in the upflow zone are responsible for extensive aqueous mobilization of sio2 aq fe and al temporal variability in the speciation and abundance of aqueous s species between 1995 and 2006 at the desmos vent field suggests an increase in the relative abundance of so2 in the magmatic end member that has mixed with seawater in the subsurface results of this study constrain processes responsible for the formation of hot spring fluids in magmatically active back arc environments and the resulting chemical exchange between the lithosphere and water column

volcanic and hydrothermal processes in submarine calderas the kulo lasi example sw pacific abstract the study area is located at the transition between the northern end of the tonga trench and the north fiji fracture zone where tectonic movements are reputed to be the fastest in the world to the southeast of futuna island a broad area of volcanism occurs within a region characterized by a change in the tectonic fabric between a ne sw oriented volcanic graben and the n s oriented alofi ridge in 2010 the active volcano kulo lasi which represents the most recent volcanic episode in the futuna area was discovered in the center of this extensive volcanic zone kulo lasi is a 20 km diameter shield volcano that rises 400 m above the seafloor it is composed of basaltic to trachy andesitic lava with no obvious geochemical affinity with the tonga subduction that occurs 500 km to the east the central caldera is 5 km in diameter and 300 m deep and is located at a water depth of 1500 m diving operations with the submersible nautile and high resolution auv mapping have revealed the presence of numerous active and inactive hydrothermal fields on the floor and the walls of the caldera four tectono volcanic stages can be distinguished at kulo lasi caldera in stage 1 the shield volcano is built annular reverse faults develop at the summit and control circulation of water rock dominated hydrothermal fluids and high temperature alteration of rocks along the nascent normal faults mixing of hydrothermal fluids with seawater is favored along normal superficial faults leading to the formation of low temperature fe mn mineralization at the summit of the volcano during stage 2 the caldera collapse gradually revealing outcrops of the altered and mineralized zones formed during stage 1 as the magma chamber cools and collapses less heat is available as a result medium to low temperature

fluid mixing and thermal regimes beneath the pacmanus hydrothermal field papua new guinea helium and oxygen isotope data abstract fluid mixing processes and thermal regimes within the snowcap and roman ruins vent sites of the pacmanus hydrothermal system papua new guinea were investigated using 3he 4he ratios from fluid inclusions within pyrite and anhydrite and the 18o signature of anhydrite depressed 3he 4he ratios of 0 2 6 91ra appear to be caused by significant atmospheric diffusive exchange whilst he ne diffusive fractionation precludes correction using 20ne 40ar 36ar ratios of 295 310 are elevated above seawater indicating the majority of argon is seawater derived but with a magmatic component 18o anhydrite ratios are 6 5 to 11 for snowcap and 6 4 to 11 9 for roman ruins using oxygen isotope fractionation factors for the anhydrite water system the temperatures calculated assuming isotopic equilibrium at depth are up to 100 c cooler than fluid inclusion trapping temperatures it is likely that anhydrite is precipitated rapidly preventing 18o equilibration by comparing new 18o values for anhydrite with corresponding published 87sr 86sr ratios seawater is inferred to penetrate deep into the snowcap system with little conductive heating a simple fluid mixing model has been constructed whereby the differing venting styles can be explained by a plumbing system at depth which favors delivery of end member hydrothermal fluid to the high temperature sites

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

the origin of hydrothermal chlorite and anhydrite rich sediments in the middle okinawa trough east china sea abstract during the integrated ocean drilling program iodp expedition 331 five sites were drilled into the iheya north knoll hydrothermal system in the okinawa trough ot a back arc basin characterized by thick terrigenous sediment following up on the previous study by shao et al 2015 we present new mineralogical geochemical and sr nd isotope data to investigate the origin of the hydrothermal sediments and characterize the hydrothermal system the substrate at the iheya north knoll is dominated by pumiceous sediment and other volcanoclastic materials interbedded with hemipelagic terrigenous and biogenous sediments impermeable layers separate the hydrothermal sediments into distinct units with depth that are characterized by various assemblages of alteration materials including polymetallic sulfides sulfates chlorite and kaolinite rich sediments the rare earth elements rees and nd isotope data suggest that the chlorite rich and kaolinite rich layers primarily resulted from the alteration of pumiceous materials in different chemical and physical conditions kaolinite rich sediment likely reflects low ph and low mg concentration fluids while chlorite rich sediment formed from fluids with high ph and increased mg contents likely at higher temperatures the sr isotopic compositions of subsurface anhydrite reflect high seawater hydrothermal fluid ratios in the mid ot hydrothermal area compared with chlorite rich sediments from other sediment covered or felsic hosted hydrothermal systems the chlorite rich sediments in the mid ot are characterized by lower concentrations of al and fe but much higher y zr hf th and rees indicative of the distinct nature of the precursor rocks in this region

3d reconstruction of volcanic and ore forming environments of a giant vms system a case study from the kidd creek mine canada abstract the archean north rhyolite is a bimodal suite of rocks located directly northwest of but structurally separate from the kidd creek volcanogenic massive sulfide deposit which has produced 140 4 million tonnes of ore grading 2 29 wt cu 6 15 wt zn 0 22 pb and 86 2 g t ag the stratigraphy of the north rhyolite is identical to that of the kidd creek mine consisting from oldest to youngest of ultramafic flows aphyric rhyolite quartz porphyritic rhyolite and basalt flows divisible into a low tio2 basalt unit 1 55 wt with minor interflow graphitic argillites the north rhyolite is interpreted to be the folded continuation of the kidd creek mine stratigraphy similar alteration patterns in the north rhyolite and the kidd creek mine stratigraphy as well as significant copper and zinc values within the thickest portions of rhyolite domes and ridges of the north rhyolite suggests the potential for economically significant mineralization within the north rhyolite stratigraphy correlation between alteration mineralization and the rhyolite domes and ridges demonstrate the volcanic structures through which the rhyolite was extruded also acted as hydrothermal fluid pathways and were controlling structures in ore formation a 3d volcanic reconstruction showing the paleo seafloor at the time of ore formation illustrates that the rhyolite flows of the north rhyolite were emplaced into the same subsidence structure as the strata of the kidd creek mine area this 3d model generated by translating complex geological data acquired through core logging and underground mapping indicates the volcanic setting of and ore forming environment at kidd creek is much larger than previously thought and provides new spatial data that can be used in exploration targeting

characterization of neoformed illite from hydrothermal experiments at 250 degrees c and p sub v soln an hrtem atem study solid products from hydrothermal experiments conducted at 250 c and p sub v soln were characterized by powder x ray diffraction xrd and atem hrtem experiments were conducted with muscovite kaolinite and quartz or amorphous silica in 2m kcl solutions for 43 to 176 d post experiment solution compositions lie either within the illite 0 88 k stability field or on the illite 0 88 k kaolinite or illite 0 88 k diaspore univariant boundaries in log a sub k sup a sub h sup vs log a sub h sub 4 sio sub 4 activity space transmission electron microscopy tem observations of muscovite grain edges reveal the neoformation of illite crystals with a range of compositions atem from 0 31 to 0 89 k o sub 10 oh sub 2 the range of k contents appears to narrow toward 0 88 k o sub 10 oh sub 2 with increased experiment duration hrtem suggests the presence of 2 to 11 layer fundamental particles composed of illitic layers with 10 a periodicity fundamental particle thicknesses increase toward an average of 8 layers particle with increased experiment duration in the longer duration experiments fundamental particle thicknesses were normally distributed about thicknesses of 4 and 8 layers whereas fundamental particles with thicknesses 4 layers were common in a shorter duration experiment the compositions and structure of the illites are consistent with the multiphase model which more states that the smectite to illite transition occurs through the step wise formation of solubility controlling phases consisting of fundamental particles with thicknesses of 1 2 4 and le 8 layers the increase in k content and fundamental particle thickness with the extent of reaction suggests that the illite crystals underwent a prograde reaction culminating in the formation of end member illite 0 88 k o sub 10 oh sub 2 this reaction in conjunction with the previously observed retrograde reaction from muscovite to end member illite demonstrates the stability of end member illite in the system k sub 2 o al sub 2 o sub 3 sio sub 2 h sub 2 o at 250 c less

hydrothermally precipitated mixed layer illite smectite in recent massive sulfide deposits from the sea floor mixed layer illite smectite i s in recent massive sulfide deposits from a seamount near the east pacific rise has been studied by x ray powder diffraction xrd and scanning and transmission electron microscopy sem tem the i s fills pore space between quartz and sulfides and xrd and tem analyses indicate that the i s contains 25 45 smectite with r1 type ordering isisis microprobe and analytical electron microscope analyses indicate a rectorite like composition k being the dominant interlayer cation the occurrence of the i s within a hydrothermally precipitated sulfide deposit the pore filling texture and the internal structure of the i s are all consistent with direct precipitation from hydrothermal solutions direct precipitation of i s from solution has two important implications first some sericite in ancient volcanogenic massive sulfide deposits may have similarly originated as hydrothermal precipitates rather than as alteration products with implications for mobility and transport of al second direct precipitation of r1 ordered i s from fluid implies that during diagenetic evolution of smectite to illite the sequence of smectite random i s ordered i s illite may not be followed

acidic and sulfate rich hydrothermal fluids from the manus back arc basin papua new guinea hot 88 120 c and acidic ph 2 1 hydrothermal fluids rich in sulfate were discovered venting in the desmos caldera depth 1926 m eastern manus back arc basin bismarck sea surrounded by papua new guinea the abundant sulfate 32 8 m m higher than the seawater value of 28 m m with elemental sulfur deposition around the vents and remarkably low d h 2 o and 34 s h 2 s values 8 1 and 5 6 respectively are suggestive of the incorporation of a magmatic fluid and the disproportionation of the exsolved so 2 from a magma body the desmos fluid may be similar in origin to the acidic sulfate chloride hot springs associated with subaerial volcanic activity in contrast to the typical hydrothermal end member mg concentration of 0 the desmos fluids are rich in mg 46 52 m m probably because of mg dissolution by acid attack upon magnesium silicate minerals

summer temperature reconstruction on the central tibetan plateau during 1860 2002 derived from annually resolved ice core pollen 1 we present a 140 year ice core pollen record with annual time resolution from the puruogangri ice field in the central tibetan plateau a linear regression model between the sum of the steppe and meadow pollen taxa and summer temperature at naqu accounts for 66 of the summer temperature variance for the period 1955 2002 on the basis of this model we reconstructed summer temperature history for the central tibetan plateau from 1860 to 2002 three marked warm periods during the 1870s 1890s and 1990s and five cold periods during the 1860s 1880s 1900s 1950s and 1960 1970s were identified within the last 100 years late 20th century warming is distinctive and may have had a major role in the present retreat of most glaciers on the tibetan plateau the pollen record is also significantly correlated with average annual temperatures over the whole tibetan plateau suggesting that these proxy data have the potential for reflecting large scale regional temperature change the statistically significant similarity between the puruogangri ice core pollen record and the 18o time series indicates that both are reliable indicators of temperature change at annual to multiyear timescales in this region

rare earth element abundances in hydrothermal fluids from the manus basin papua new guinea indicators of sub seafloor hydrothermal processes in back arc basins abstract rare earth element ree concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the manus back arc basin vienna woods pacmanus desmos and susu knolls vent areas sampled vent fluids show a wide range of absolute ree concentrations and chondrite normalized reen distribution patterns lan smn 0 6 11 lan ybn 0 6 71 eu n eu n 1 55 reen distribution patterns in different vent fluids range from light ree enriched to mid and heavy ree enriched to flat and have a range of positive eu anomalies this heterogeneity contrasts markedly with relatively uniform reen distribution patterns of mid ocean ridge hydrothermal fluids in manus basin fluids aqueous ree compositions do not inherit directly or show a clear relationship with the ree compositions of primary crustal rocks with which hydrothermal fluids interact these results suggest that the rees are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of rees in submarine hydrothermal fluids in contrast differences in aqueous ree compositions are consistently correlated with differences in fluid ph and ligand chloride fluoride and sulfate concentrations our results suggest that the rees can be used as an indicator of the type of magmatic acid volatile i e presence of hf so2 degassing in submarine hydrothermal systems additional fluid data suggest that near seafloor mixing between high temperature hydrothermal fluid and locally entrained seawater at many vent areas in the manus basin causes anhydrite precipitation anhydrite effectively incorporates ree and likely affects measured fluid ree concentrations but does not affect their relative distributions

geochemistry of hydrothermal fluids from the pacmanus northeast pual and vienna woods hydrothermal fields manus basin papua new guinea abstract processes controlling the composition of seafloor hydrothermal fluids in silicic back arc or near arc crustal settings remain poorly constrained despite growing evidence for extensive magmatic hydrothermal activity in such environments we conducted a survey of vent fluid compositions from two contrasting sites in the manus back arc basin papua new guinea to examine the influence of variations in host rock composition and magmatic inputs both a function of arc proximity on hydrothermal fluid chemistry fluid samples were collected from felsic hosted hydrothermal vent fields located on pual ridge pacmanus and northeast ne pual near the active new britain arc and a basalt hosted vent field vienna woods located farther from the arc on the manus spreading center vienna woods fluids were characterized by relatively uniform endmember temperatures 273 285 c and major element compositions low dissolved co 2 concentrations 4 4 mmol kg and high measured ph 4 2 4 9 at 25 c temperatures and compositions were highly variable at pacmanus ne pual and a large newly discovered vent area fenway was observed to be vigorously venting boiling 358 c fluid all pacmanus fluids are characterized by negative d h 2 o values in contrast to positive values at vienna woods suggesting substantial magmatic water input to circulating fluids at pual ridge low measured ph 25 c values 2 6 2 7 high endmember co 2 up to 274 mmol kg and negative 34 s h 2 s values down to 2 7 in some vent fluids are also consistent with degassing of acid volatile species from evolved magma dissolved co 2 at pacmanus is more enriched in 13 c 4 1 to 2 3 than vienna woods 5 2 to 5 7 suggesting a contribution of slab derived carbon the mobile elements e g li k rb cs and b are also greatly enriched in pacmanus fluids reflecting increased abundances in the crust there relative to the manus spreading center variations in alkali and dissolved gas abundances with cl at pacmanus and ne pual suggest that phase separation has affected fluid chemistry despite the low temperatures of many vents in further contrast to vienna woods substantial modification of pacmanus ne pual fluids has taken place as a result of seawater ingress into the upflow zone consistently high measured mg concentrations as well as trends of increasingly non conservative so 4 behavior decreasing endmember ca cl and sr cl ratios with increased mg indicate extensive subsurface anhydrite deposition is occurring as a result of subsurface seawater entrainment decreased ph and endmember fe mn ratios in higher mg fluids indicate that the associated mixing cooling gives rise to sulfide deposition and secondary acidity production several low temperature 80 c fluids at pacmanus ne pual also show evidence for anhydrite dissolution and water rock interaction fixation of b subsequent to seawater entrainment hence the evolution of fluid compositions at pual ridge reflects the cumulative effects of water rock interaction admixing and reaction of fluids exsolved from silicic magma phase separation segregation and seawater ingress into upflow zones

alteration and mineralization of an oceanic forearc and the ophiolite ocean crust analogy mineralogical chemical and isotopic o c s and sr analyses were performed on minerals and bulk rocks from a forearc basement section to understand alteration processes and compare with mid ocean ridges mor and ophiolites ocean drilling program hole 786b in the izu bonin forearc penetrates 103 m of sediment and 725 m into volcanic flows breccias and basal dikes the rocks comprise boninites and andesites to rhyolites most of the section was affected by low temperature 100 c seawater alteration with temperatures increasing downward the rocks are partly 5 25 altered to smectite fe oxyhydroxide calcite and phillipsite and exhibit gains of k rb and p loss of ca variable changes in si na mg fe sr and y and elevated 18o and 87sr 86sr higher temperatures 150 c in the basal dikes below 750 m led to more intense alteration and formation of chlorite smectite corrensite albite k feldspar and quartz chlorite a 5 m thick hydrothermally altered and pyritized zone at 815 m in the basal dikes reacted with mixtures of seawater and hydrothermal fluids to mg chlorite albite and pyrite and gained mg and s and lost si and ca focused flow of hydrothermal fluids produced serialization halos na k sericite quartz pyrophyllite k feldspar and pyrite along quartz veins at temperatures of 200 250 c high 87sr 86sr ratios of chloritized 0 7055 and sericitized 0 7065 rocks indicate involvement of seawater via mixing with hydrothermal fluids low 34s of sulfide 2 to 5 5 and sulfate 12 5 are consistent with input of magmatic so2 into hydrothermal fluids and disproportionation to sulfide and sulfate alteration processes were generally similar to those at mors but the arc section is more intensively altered in part because of the presence of abundant glassy rocks and mafic phases the increase in alteration grade below 750 m and the mineralization in the basal dikes are analogous to changes that occur near the base of the volcanic section in mor and the troodos ophiolite

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

insights to magmatic hydrothermal processes in the manus back arc basin as recorded by anhydrite microchemical analyses of rare earth element ree concentrations and sr and s isotope ratios of anhydrite are used to identify sub seafloor processes governing the formation of hydrothermal fluids in the convergent margin manus basin papua new guinea samples comprise drill core vein anhydrite and seafloor massive anhydrite from the pacmanus roman ruins snowcap and fenway and susu knolls north su active hydrothermal fields chondrite normalized ree patterns in anhydrite show remarkable heterogeneity on the scale of individual grains different from the near uniform ree n patterns measured in anhydrite from mid ocean ridge deposits the ree n patterns in anhydrite are correlated with ree distributions measured in hydrothermal fluids venting at the seafloor at these vent fields and are interpreted to record episodes of hydrothermal fluid formation affected by magmatic volatile degassing 87 sr 86 sr ratios vary dramatically within individual grains between that of contemporary seawater and that of endmember hydrothermal fluid anhydrite was precipitated from a highly variable mixture of the two the intra grain heterogeneity implies that anhydrite preserves periods of contrasting hydrothermal versus seawater dominant near seafloor fluid circulation most sulfate 34 s values of anhydrite cluster around that of contemporary seawater consistent with anhydrite precipitating from hydrothermal fluid mixed with locally entrained seawater sulfate 34 s isotope ratios in some anhydrites are however lighter than that of seawater which are interpreted as recording a source of sulfate derived from magmatic so 2 degassed from underlying felsic magmas in the manus basin the range of elemental and isotopic signatures observed in anhydrite records a range of sub seafloor processes including high temperature hydrothermal fluid circulation varying extents of magmatic volatile degassing seawater entrainment and fluid mixing the chemical and isotopic heterogeneity recorded in anhydrite at the inter and intra grain scale captures the dynamics of hydrothermal fluid formation and sub seafloor circulation that is highly variable both spatially and temporally on timescales over which hydrothermal deposits are formed microchemical analysis of hydrothermal minerals can provide information about the temporal history of submarine hydrothermal systems that are variable over time and cannot necessarily be inferred only from the study of vent fluids

contrasting evolution of hydrothermal fluids in the pacmanus system manus basin the sr and s isotope evidence ocean drilling program odp leg 193 investigated two sites of hydrothermal activity along the crest of the pual ridge in the eastern manus basin a site of low temperature diffuse venting snowcap site 1188 and a high temperature black smoker site roman ruins site 1189 were drilled to depths of 386 and 206 m below seafloor mbsf respectively although the two sites are 1000 m apart the 87sr 86sr and 34s signatures of anhydrite recovered at both sites are very different the data suggest a complex interplay among hydrothermal fluid magmatic fluid and seawater during alteration and mineralization of the pacmanus papua new guinea australia canada manus system these new results significantly expand the subsurface data on seafloor hydrothermal systems and may begin to explain the earliest processes of multistage mineralization and alteration history that typify ancient massive sulfide systems

genesis of kaolin minerals and pyrophyllite in kuroko deposits of japan implications for the origins of the hydrothermal fluids from mineralogical and stable isotope data hydrogen and oxygen isotope and x ray analyses were performed on kaolin minerals kaolinite dickite and nacrite and pyrophyllite from the minamishiraoi and inarizawa deposits of northern japan dickite nacrite and mica rich micasmectite mixed layer minerals occur as envelopes around barite sulfide orebodies in the footwall alteration zones of the minamishiraoi and inarizawa deposits while kaolinite and smectite rich micasmectite mixed layer minerals occur in the outer alteration zones away from the orebodies the hydrogen and oxygen isotope ratios of kaolin minerals from the minamishiraoi and inarizawa deposits fall in a narrow range of 24 to 32 for hydrogen and 7 8 to 9 9 for oxygen these isotope ratios indicate that the hydrothermal fluid responsible for kaolin formation was the same as that which caused mineralization the 18o values of kaolin minerals of the minamishiraoi deposit increase in order of nacrite dickite kaolinite this trend indicates that nacrite formed at the highest temperature among the three kaolin polytypes the oxygen isotope ratio of monoclinic pyrophyllite 18o 5 2 from the inarizawa deposit is lower than that of nacrite 18o 7 5 the difference of 18o values between the pyrophyllite and nacrite may be explained by a higher temperature of formation for the pyrophyllite the mineralogie and isotopic data of the footwall alteration halos are useful as indicators of the size and metal contents of kuroko orebodies the footwall alteration halo of the minamishiraoi deposit small size and barite rich deposit contains kaolin and micasmectite mixed layer minerals while those of the larger polymetallic kuroko deposits contain seriate and chlorite thermodynamic data of these clay minerals indicate that the minamishiraoi deposit formed at relatively lower temperature and farther from the heat source than larger polymetallic deposits the chemical data for hydrothermal solutions from the 13 n east pacific rise hydrothermal site as presented in the literature plot in the kaolinite stability field at 150 c or less therefore active submarine hydrothermal systems such as 13 n east pacific rise should form kaolin minerals in the alteration halo as long as the temperature of the hydrothermal fluid is below sericite and chlorite stability

fluid inclusion evidence for subsurface phase separation and variable fluid mixing regimes beneath the deep sea pacmanus hydrothermal field manus basin back arc rift papua new guinea 1 altered volcanic rocks were cored from over 350 m below the seafloor at the papua new guinea australia canada manus basin hydrothermal field pacmanus deep sea hydrothermal field in the eastern manus back arc basin fluid inclusions in anhydrite veins reveal phase separation and fluid mixing beneath the seafloor the anhydrite precipitated from high temperature fluids 150 385 c at roman ruins a site of active high temperature venting 220 276 c measured by submersible the fluid inclusion thermal depth profile is uniform and high temperature 242 368 c at snowcap a site of warm water effusion 6 65 c the fluid inclusions indicate high temperatures at depth 270 385 c but both low and high temperatures in the shallower section this indicates a flow regime dominated by vertical advection and shallow entrainment and mixing with cool seawater inclusions at snowcap exhibit extreme salinity variations due to phase separation at temperatures above 350 c fluids contain na cl fe zn mg and ba and a minor gas component such as co2 or ch4 most inclusions at roman ruins exhibit salinities that fall within the range of those observed at modern active vent sites along the mid ocean ridge system fluid inclusion temperatures support a hypothesis developed previously from sr isotopic analysis that the subseafloor at snowcap is characterized by mixing between deep sourced hot hydrothermal fluids and cold seawater like fluid both heating of seawater and cooling of upwelling hydrothermal fluids can be recognized by combining isotopic and fluid inclusion data in contrast to snowcap the regime at roman ruins is less varied with uniformly high temperature upwelling fluids that have hydrothermally dominated sr isotopic ratios

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania the western sahara desert in mauritania is dominated by extensive sand seas consisting largely of linear dunes analyses of landsat images geomorphic and stratigraphic studies and optically stimulated luminescence dating of dunes in the azefal agneitir and akchar sand seas provide evidence that three main generations of dunes were formed during the periods 25 15 ka centered around the last glacial maximum 10 13 ka spanning the younger dryas event and after 5 ka the wind regimes that occurred during each of these periods were significantly different leading to the formation of dunes on three distinct superimposed trends northeast north northeast and north and the development of the sand seas as composite geomorphic features

chemical sedimentary protoliths in the 3 75 ga nuvvuagittuq supracrustal belt quebec canada abstract analyses of chemical sedimentary precipitates such as banded iron formation bif provide a direct means to explore the nature and composition of the early hydrosphere the recently discovered 3750 myr old nuvvuagittuq supracrustal belt nsb in the northeast superior province quebec canada hosts a suite of iron oxide rich pyroxene and amphibole units that are interpreted to be the metamorphosed equivalents of fe oxide facies bif and a collection of bif like ca fe mg silicate rocks the nsb rocks provide a rare glimpse of trace metal availability in eoarchean ca 3800 ma seawater as they may be contemporaneous with the relatively well studied isua supracrustal belt of southern west greenland their comparison provides an opportunity to enhance our basic understanding of the eoarchean oceans at a global scale work since the initial discovery of the nsb in 2001 has established the basic lithological geochemical and petrographic characteristics of these bif and bif like rocks here we review the current state of knowledge of nsb rocks of probable chemical sedimentary origin including aspects of their geology likely origin and age we conclude by examining the implications of results thus far for our understanding of early seawater compositions and for the emergence of life in the context of early metallo enzyme evolution

application of b mg li and sr isotopes in acid sulfate vent fluids and volcanic rocks as tracers for fluid rock interaction in back arc hydrothermal systems

developmental characteristics of aeolian dunes and environmental changes in the adjoining region of puruogangri ice sheet north tibetan plateau a large area of moraine sediments and cryogenic weathering products formed by glacial action and a cold environment are the main source of aeolian sand in the high and cold region of the qinghai tibetan plateau in china the evolution of aeolian dunes is closely related to the periglacial environment owing to the freezing of dune land surfaces the evolution of sand dunes is dominated by expanding dune bases and vertical accretion thereby forming large barchan dunes the migration rates of these large barchan dunes are very slow at an average rate of 1 7 0 7 cm a 1 the temperature mainly controls the environmental changes in the adjoining region of puruogangri ice sheet the 14c dating of humus layers in the studied area of the sand dune are 10 780 130 9 549 130 8 320 110 7 450 100 5 970 95 5 330 90 4 420 80 3 460 80 2 280 70 980 70 abp respectively the region s high temperature rising up during summer from the southwest monsoon intensity might be an important factor as long as both water and temperature conditions are suitable the plants will grow well sand dunes will be stabilized forming humus layers otherwise sand dunes are bare and re activate

heating and freezing experiments on aqueous fluid inclusions in anhydrite recognition and effects of stretching and the low temperature formation of gypsum aqueous fluid inclusions in anhydrite that are frozen during microthermometry commonly develop new daughter crystals heating these inclusions induces the new daughter crystals to decompose repeated cycles of crystal growth and decomposition may result in morphological changes of the fluid inclusions this phenomenon of new mineral growth presumed to represent the low temperature hydrate gypsum has been recognized for over 20 years nevertheless its occurrence and its significance to the determination of inclusion salinities are not widely appreciated similarly the potential of inclusions in anhydrite to stretch when overheated is commonly assumed yet tests demonstrating the phenomenon have not been reported changes in the ice melting temperature of aqueous inclusions in anhydrite before and after gypsum formation were documented showing that hydration of the host anhydrite may significantly lower the ice melting temperature and increase the salinity of the residual inclusion fluid heating inclusions to induce gypsum to decompose results in the release of bound water restoring the inclusions to their original salinity the homogenization temperatures of inclusions that have undergone these phenomena are generally unchanged indicating that the inclusions specific volumes are unchanged however heating aqueous inclusions in anhydrite more than ten degrees or so above their homogenization temperature commonly results in stretching therefore those who study aqueous inclusions in anhydrite must avoid the determination of ice melting temperatures if new gypsum daughter crystals are present and must determine homogenization temperatures sequentially with rising temperature to avoid overheating and stretching

drill core based facies reconstruction of a deep marine felsic volcano hosting an active hydrothermal system pual ridge papau new guinea odp leg 193 abstract pual ridge is a deep marine felsic volcanic edifice in the eastern manus back arc basin papua new guinea with an estimated volume of 6 to 9 km 3 it is 1 1 5 km wide 20 km long and rises 500 600 m above the surrounding ocean floor the active pacmanus hydrothermal field on the crest of pual ridge at 1640 1690 m below sea level was the target of ocean drilling program leg 193 variably altered dacite lavas have been recovered from the subsurface of a low t discharge site snowcap and a high t black smoker site roman ruins reaching a maximum depth of 380 m below seafloor mbsf volcanic facies interpretation of these cores is difficult due to incomplete recovery and widespread pseudoclastic textures generated by fracturing and multi phase incomplete fluid dacite interaction however distinction of genuine volcaniclastic facies and facies with alteration related clastic appearance is important in order to define paleo seafloor positions within the volcanic stratigraphy that may be prospective for massive sulfide mineralization this has been accomplished using remnant primary characteristics indicative of transportation such as polymictic composition grading or textural evidence for differential movement of individual clasts three phases of volcanic activity can be distinguished and a proximal facies association dominated by coherent facies of dacite lavas exists below snowcap at roman ruins a medial facies association consists of lava flows with about equal proportions of coherent and volcaniclastic facies endogenous growth was an important process during lava flow emplacement and groundmass textures such as perlite flow banding and spherulites indicate that cooling rates were variable locally allowing for high temperature devitrification a tube pumice breccia unit is interpreted as the resedimented facies of a quench fragmented highly vesicular dacite lava carapace sulfide accumulations in the subsurface are restricted to roman ruins suggesting that the abundance of volcaniclastic facies favored ascent of metal bearing fluids due to the inherent high permeability evidence for mineralization at paleo seafloor positions at 110 and 195 mbsf indicate a complex interrelationship between volcanic and hydrothermal activity a facies model has been developed which may help to locate subaqueous felsic lava dominated volcanic centers and associated sulfide deposits in ancient volcano sedimentary successions

mechanisms of mg phyllosilicate formation in a hydrothermal system at a sedimented ridge middle valley juan de fuca we present results of a detailed mineralogical and geochemical study of the progressive hydrothermal alteration of clastic sediments recovered at odp site 858 in an area of active hydrothermal venting at the sedimented axial rift valley of middle valley northern juan de fuca ridge these results allow a characterization of newly formed phyllosilicates and provide constraints on the mechanisms of clay formation and controls of mineral reactions on the chemical and isotopic composition of hydrothermal fluids hydrothermal alteration at site 858 is characterized by a progressive change in phyllosilicate assemblages with depth in the immediate vent area at hole 858b detrital layers are intercalated with pure hydrothermal precipitates at the top of the section with a predominance of hydrothermal phases at depth sequentially downhole in hole 858b the clay fraction of the pure hydrothermal layers changes from smectite to corrensite to swelling chlorite and finally to chlorite in three pure hydrothermal layers in the deepest part of hole 858b the clay minerals coexist with neoformed quartz neoformed and detrital components are clearly distinguished on the basis of morphology as seen by sem and tem and by their chemical and stable isotope compositions corrensite is characterized by a 24 a stacking sequence and high si and mg contents with fe fe mg ratio of 0 08 we propose that corrensite is a unique possibly metastable mineralogical phase and was precipitated directly from seawater dominated hydrothermal fluids hydrothermal chlorite in hole 858b has a stacking sequence of 14 a with fe fe mg ratios of 0 35 the chemistry and structure of swelling chlorite suggest that it is a corrensite chlorite mixed layer phase the mineralogical zonation in hole 858b is accompanied by a systematic decrease in 18o reflecting both the high thermal gradients that prevail at site 858 and extensive sediment fluid interaction precipitation of the mg phyllosilicates in the vent region directly controls the chemical and isotopic compositions of the pore fluids this is particularly evident by decreases in mg and enrichments in deuterium and salinity in the pore fluids at depths at which corrensite and chlorite are formed structural formulae calculated from tem edx analyses were used to construct clay h2o oxygen isotope fractionation curves based on oxygen bond models our results suggest isotopic disequilibrium conditions for corrensite quartz and swelling chlorite quartz precipitation but yield an equilibrium temperature of 300 c 30 for chlorite quartz at 32 m below the surface this estimate is consistent with independent estimates and indicates steep thermal gradients of 10 11 m in the vent region

the smectite chlorite transition in drillhole nj 15 nesjavellir geothermal field iceland xrd bse and electron microprobe investigations abstract in well nj 15 of the nesjavellir geothermal field iceland the transition of discrete smectite into discrete chlorite has been studied from drill cuttings recovered at depths of less than 1714 m and over a continuous range of temperatures between 60 and 300 c at temperatures below 180 c the clay fractions contain mixtures of di and trioctahedral smectites whose layer charge increases with depth between 200 and 240 c discrete smectites have transformed into smectite rich randomly interstratified chlorite and smecite r0 c s because the abundance of chlorite interlayers in this c s is generally 20 its presence can be detected only by electron microprobe techniques and not by x ray diffraction between 245 and 265 c both regularly r1 and randomly interstratified c s are the predominant layer silicates discrete chlorite first appears at approximately 270 c and coexists with minor amounts of r0 c s at higher temperatures r0 and r1 c s form a nearly complete compositional series between trioctahedral saponite and discrete chlorite end members the interlayer cation and si content of smectites and c s decrease with increasing temperature the mg mg fe content of smectite c s and chlorite is unrelated to temperature the percentage of chlorite in c s as determined by electron microprobe analyses increases continuously with increasing temperature except for occurrences of smectite rich c s in fresh basaltic dykes which have not thermally equilibrated with the higher grade country rocks

radiocarbon dating of playa lake hydrologic changes examples from northwestern china and central australia accurate radiocarbon dating of arid zone playas is restricted by shortage of suitable organic matter analyses from two large systems in australia lake frome and china qarhan playa in the qaidam basin demonstrate the problems associated with the use of carbonates for dating organic carbon although requiring treatment of large samples 1 2 kg provides the most accurate basis for establishing chronologic control in qarhan a deposit of halite averaging about 30 m thick extends over an area of 5800 km2 carbonate in the system is dominantly derived as clastics from loess transported by northwesterly winds the large component of dead carbon thus involved explains anomalous patterns of dates derived from these materials such results are consistently much older than those based on organic carbon in lake frome subject to a more maritime climate in central australia the carbonate component is dominantly authigenic lacustrine in origin contaminated by a small detrital component it provides ages about one half life older than those from organic carbon the sequence from qarhan supplemented by evidence of lacustral pluvial episodes in two other sub basins in qaidam kunteyi and xiao qaidam illustrates the presence there of expanded waterbodies persisting from at least 40 000 to about 15 000 yr b p in areas where little surface water persists today the large evaporite deposits formed between about 25 000 to sometime after 15 000 yr b p holocene climate appears to have remained hyperarid like that of today at lake frome an early lacustral phase gave way before 18 000 yr b p to drying and aeolian activity water had returned to the system by 16 000 yr b p signalling a decline if not the end of aridity lacustrine conditions persisted through early holocene with drying and development of playa facies about 7000 yr b p after a brief return to lacustrine conditions between about 6000 4000 yr b p a dry playa environment has continued to the present day the frome and qarhan playas although in comparable latitudes lie in very different climatic and tectonic settings their palaeohydrologic records are neither in phase nor in distinct anti phase emphasizing the complexity of comparing palaeoclimatic records from different circulation systems

lake evolution during the past 30 000 years in china and its implications for environmental change abstract taking china as a whole lake expansion occurred 500 b c 0 a d 650 950 a d and 1250 1650 a d over the past 3000 yr the expansions were mainly due to climatic fluctuations and correspond to frequent flood reports three regional characteristics of lake development have been recognized 1 fluctuations of near coastal lakes and those in other regions as well were out of phase during 500 b c 500 a d which possibly resulted from out of phase fluctuations of climate and sea level on 10 to 100 yr time scale 2 as the lower yellow river channel migrated southward the lakes in the south of the north china plain formed and reached their largest sizes much later than those in the north 3 for the lakes in the middle and lower yangtze river valley the higher a lake basin lies above a neighboring river and the further the lake is from the river s mouth in general the younger the lake is through land reclamation the ancient chinese have changed most of the lakes greatly however human activities were also constrained in certain ways by the natural changes of the lakes reclamation usually was banned and farmland was abandoned to repair reservoirs while lakes were expanding

gamma ray spectrometric analysis of hydrothermally altered dacite samples from the pacmanus hydrothermal field implications for the interpretation of gamma ray wireline measurements abstract spectral gamma ray wireline logging derives the concentrations of potassium thorium and uranium of the formation by measuring the gamma ray spectrum under the assumption of secular equilibrium these measurements were carried out in a number of boreholes drilled by ocean drilling program leg 193 at the pacmanus hydrothermal field spectral gamma ray logs from several of these holes show intervals of increased radioactivity associated with high uranium values of up to 60 ppm snowcap hydrothermal field and 25 ppm roman ruins hydrothermal field nine samples of hydrothermally altered dacite were analyzed using gamma spectrometry to examine the origin of elevated radioactivity and to test for distortion of secular equilibrium core spectrometry indicates that secular equilibrium is distorted distortion can be explained by either an uptake of nuclides of the lower part of the 238u decay series or by removal of 238u or 234th from the rocks in all cases wireline uranium logs and core spectrometry do not reflect true uranium concentrations of the formation but uranium is overestimated by a factor of 3 4 at roman ruins uranium values from wireline logging show higher uranium concentrations over large intervals than uranium values from core spectrometry and from published core geochemistry even when a possible leaching of uranium is taken into account wireline logs indicate that depth intervals of increased radioactivity are related to the occurrence of stockwork mineralization in these depth intervals core recovery was extremely low in addition to the distortion of secular equilibrium low core recovery and preferential loss of softer and more altered material cause a sampling bias between core samples and wireline data and may explain the observed difference in uranium concentrations between core and wireline logs

the subseafloor thermal gradient at iheya north knoll okinawa trough based on oxygen and hydrogen isotope ratios of clay minerals abstract we measured the oxygen and hydrogen isotope ratios of smectite chlorite and illite in hydrothermally active sediments at the iheya north knoll okinawa trough obtained by seafloor drilling of active hydrothermal fields during the integrated ocean drilling program iodp expedition 331 formation temperatures calculated from oxygen isotope data were compared to the downhole temperatures that were measured during the same expedition the 18o values ranged from 9 9 to 13 3 for smectite 1 3 to 3 0 for chlorite or chlorite smectite mixed layer mineral and 2 1 to 5 1 for illite or illite smectite mixed layer mineral with minor chlorite for samples of illite that contained minor chlorite 18o values for illite or illite smectite mixed layer mineral of 4 4 to 6 1 were calculated based on the proportion of the two clay minerals calculated from chemical composition of the individual mineral and the mixture determined by tem eds and epma we estimated the formation temperatures of the minerals using oxygen isotope fractionation data and assumed values of 0 to 1 2 for the fluid that was equilibrated with the minerals based on the reported values of the seawater and vent fluid measured in previous studies the temperature range calculated was 111 175 c for a shallow layer less than about 25 m below seafloor mbsf that contained smectite and a minor kaolinite component 177 297 c for a deeper layer between about 25 and 40 mbsf that was dominated by chlorite or chlorite smectite mixed layer mineral and 220 314 c for the deepest layer between about 40 and 120 mbsf that contained illite or illite smectite mixed layer mineral with less chlorite the temperatures of mineral formation calculated from the oxygen stable isotope data were slightly higher at some depths but both calculated and measured temperatures demonstrated a steep step wise thermal gradient below the active hydrothermal field where temperatures of 200 c were determined at as little as 50 mbsf hydrogen isotope values mostly ranged between 40 and 55 and did not vary significantly or systematically between the layers except in the clay fractions containing smectite above 25 mbsf that had relatively low values between 65 and 72 hydrogen isotope results of the clay minerals were problematic to interpret and not consistent with interpretation of the oxygen data calculated temperatures from illite and smectite were mostly negative whereas temperatures calculated from chlorite were more positive average 145 c but lower than those from the oxygen isotope data additional work is still required to determine the hydrogen isotope fractionation between clay minerals and water with respect to temperature

thermal diagenesis of clay minerals within volcanogenic material from the tonga convergent margin abstract clay minerals are examined in detail in the sediment from the tonga trench margin at site 841 leg 135 odp the changes in amount and nature of secondary clays with depth provide an alternative explanation for the intensive alteration of volcanogenic material at convergent margins a characteristic distribution of clay minerals with depth shows four distinct zones unexplainable by simple burial diagenesis processes these are named the upper reactive lower and rhyolitic zones the reactive zone is intercalated with numerous sills and is characterized by the dominant iron rich clays such as saponite corrensite and chlorite associated with analcime the occurrence of such iron rich clays mostly associated with a large amount of analcime yields chemical and mineralogical evidence for thermal diagenesis the required heat for the diagenetic process was transferred from recently intruded basaltic andesite sills in the vicinity of these intrusions the iron rich clay minerals may have formed at temperatures up to 200 c a zoning with respect to clay and zeolite minerals indicates that the influence of the palaeoheat flow decreased with the distance from the intrusion the formation of interlayered i s illite kaolinite and aluminous chlorite which are recognized as major secondary minerals within the rhyolitic complex was mainly controlled by both early diagenesis at moderately elevated temperatures and since the eocene by burial diagenesis at low temperatures the occurrence of a steam zone in an early stage of the intrusion is restricted to miocene tuffs and has overprinted the early alteration of the volcanogenic material within the tuffs and has changed the originally pristine composition of the pore fluids

mineralogical geochemical and isotopic characteristics of hydrothermal alteration processes in the active submarine felsic hosted pacmanus field manus basin papua new guinea during odp leg 193 4 sites were drilled in the active pacmanus hydrothermal field on the crest of the felsic pual ridge to examine the vertical and lateral variations in mineralization and alteration patterns we present new data on clay mineral assemblages clay and whole rock chemistry and clay mineral strontium and oxygen isotopic compositions of altered rocks from a site of diffuse low temperature venting snowcap site 1188 and a site of high temperature venting roman ruins site 1189 in order to investigate the water rock reactions and associated elemental exchanges the volcanic succession at snowcap has been hydrothermally altered producing five alteration zones 1 chlorite illite cristobalite plagioclase alteration apparently overprinted locally by pyrophyllite bleaching at temperatures of 260 310degreesc 2 chlorite mixed layer clay alteration at temperatures of 230degreesc 3 chlorite and illite alteration 4 illite and chlorite illite mixed layer alteration at temperatures of 250 260degreesc and 5 illite chlorite alteration at 290 300degreesc felsic rocks recovered from two holes 1189a and 1189b at roman ruins although very close together show differing alteration features hole 1189a is characterized by a uniform chlorite illite alteration formed at similar to250degreesc overprinted by quartz veining at 350degreesc in contrast four alteration zones occur in hole 1189b 1 illite chlorite alteration formed at similar to300degreesc 2 chlorite illite alteration at 235degreesc 3 chlorite illite and mixed layer clay alteration and 4 chlorite illite alteration at 220degreesc mass balance calculations indicate that the chloritization illitization and bleaching silica pyrophyllite assemblages alteration stages are accompanied by different chemical changes relative to a calculated pristine precursor lava the element cr appears to have a general enrichment in the altered samples from pacmanus the clay concentrate data show that cr and cu are predominantly present in the pyrophyllites illite shows a significant enrichment for cs and cu relative to the bulk altered samples considerations of mineral stability allow us to place some constraints on fluid chemistry hydrothermal fluid ph for the chloritization and illitization was neutral to slightly acidic and relatively acidic for the pyrophyllite alteration in general the fluids especially from roman ruins and at intermediate depths below snowcap show only a small proportion of seawater mixing 10 fluids in shallow and deep parts of the snowcap holes in contrast show stronger seawater influence copyright c 2004 elsevier ltd

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

asian summer monsoon instability during the past 60 000 years magnetic susceptibility and pedogenic evidence from the western chinese loess plateau abstract the 28 m high resolution shajinping loess section in lanzhou on the western chinese loess plateau records a 60 ka millennial summer monsoon variation the record shows that asian summer monsoons have rapid episodic pulse enhancements spanning only ca 1 2 ka in high frequency domain and having sub milankovitch cycles of progressive weakening in low frequency domain in the last glaciation soil formation seems to occur with a surprisingly fast response to these summer monsoon enhancements resulting in weakly or moderately developed paleosol sequences both the pattern and timing of the summer monsoon enhancements show that they can be correlated to most major warm dansgaard oeschger episodes and long term cooling bond cycles of the north atlantic climatic records indicating a possible teleconnection between tropic oceanic air masses and the north atlantic climatic system but differences exist for the transition of mis 2 3 and the holocene where extraordinarily heavy dust input events and fairly variable climatic fluctuations occur for the former and latter respectively a westerlies swing model is proposed to interpret this link

phyllosilicate alteration mineral assemblages in the active subsea floor pacmanus hydrothermal system papua new guinea odp leg 193 pacmanus is an active submarine hydrothermal system in the manus back arc basin papua new guinea located at 1 600 to 1 700 m below sea level on the crest of a dacitic volcano it is inferred to represent a modern analogue of ancient mineralizing sea floor hydrothermal systems that produced volcanogenic polymetallic massive sulfide deposits ocean drilling program odp leg 193 drilled the subsea floor hydrothermal alteration zone of pacmanus in a high temperature discharge area roman ruins and a low temperature discharge area snowcap reaching a maximum depth of 380 m below the sea floor evidence from short wavelength infrared swir spectroscopy x ray diffraction xrd analyses calculated normative mineral abundances and electron microprobe data show that there are substantial variations in the hydrothermal phyllosilicate assemblages within the pacmanus hydrothermal system the altered dacite at roman ruins contains 10 to 25 wt percent normative chlorite smectite and up to 15 wt percent normative illite in contrast altered dacite below snowcap contains up to 50 wt percent combined normative illite paragonite chlorite smectite pyrophyllite swir data show that pyrophyllite is particularly abundant between 50 and 120 and between 220 and 270 m below sea floor indicating localized interaction of dacite with acidic hydrothermal fluids variations in the na k ratio of dioctahedral phyllosilicate determined by electron microprobe and spectral analyses confirm the presence of a paragonitic component at snowcap a model is suggested to explain the differences in the distribution of hydrothermal phyllosilicate assemblages in the two areas in terms of variations in fluid composition and changes to the subsea floor hydrology in a dynamically evolving volcanic hydrothermal environment

textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine pacmanus hydrothermal system eastern manus basin variably altered dacite from the pacmanus vent field in the eastern manus back arc basin papua new guinea was studied to determine the textural and mineralogical characteristics of hydrothermal alteration taking place in the immediate subsurface of this modern seafloor hydrothermal system detailed textural investigations show that fluid flow through the glassy dacite has been strongly controlled by the primary volcanic textures quench fractures and networks of interconnected perlitic cracks linking vesicles provided pathways for hydrothermal fluids flowing up to the seafloor hydrothermal alteration along these pathways resulted in the formation of pseudoclastic textures textural evidence suggests that alteration of the glassy dacite has not been sustained the samples have been affected by incipient hydrothermal alteration that is typically not preserved in ancient volcanic rock hosted massive sulfide deposits interaction of the glassy dacite with hydrothermal fluids primarily resulted in the conversion of volcanic glass to dioctahedral smectite only minor amounts of trioctahedral smectite were formed destruction of the volcanic glass and the formation of smectite caused pronounced changes in the chemistry of the dacite samples in particular a decrease in the sio2 whole rock content and the na2o k2o ratio the two alkali elements behaved differently during hydrothermal alteration due to preferential incorporation of k into the interlayer position of the newly formed dioctahedral smectite smectite formation occurred under rock dominated conditions although the addition of mg was required to form trioctahedral smectite from the silicic volcanic glass primary plagioclase was resistant to hydrothermal alteration highlighting the fact that the destruction of volcanic glass and feldspar are not necessarily contemporaneous in massive sulfide forming hydrothermal systems incipient alteration of the glassy dacite close to the seafloor occurred at temperatures below 150 c in an environment that allowed the development of steep temperature gradients comparison of the new data to the findings of deep drilling during odp leg 193 suggests that the smectite rich alteration in the immediate subsurface of the pacmanus hydrothermal vent field represents the low temperature equivalent of illite and chlorite rich alteration associations forming in the upflow zones of the hydrothermal fluids in the deeper portion of the volcanic sequence

geochemistry of hot springs at the susu knolls hydrothermal field eastern manus basin advanced argillic alteration and vent fluid acidity abstract susu knolls is an area of ongoing magmatic activity and recent volcanism located in the back arc spreading environment of the manus basin in the bismarck sea papua new guinea in 2006 hydrothermal fluids were collected from three areas of submarine hot spring venting and analyzed for the chemical and isotopic composition of major and trace species fluids were characterized by temperatures that varied from 226 325 c and formed grey to black smoke as they mixed with bottom seawater the compositions of seawater derived vent fluids are regulated by the relative contributions of fluid rock and fluid sediment interaction phase separation and the addition of volatiles from magmatic degassing in addition to phase separation leaching of cl from felsic rocks that compose the lithosphere in back arc environments may produce cl concentrations in excess of seawater values the measured ph25 c of susu knolls smoker fluids varied from 1 5 3 7 a range that includes values substantially more acidic than typically observed in fluids at mid ocean ridge spreading centers late stage addition of magmatic volatiles in the shallow seafloor is directly responsible for the most acidic fluids ph25 c values below 2 in contrast the acidity of vent fluids characterized by ph25 c values between 2 and 3 is not the direct result of the direct addition of magmatically derived acidic species instead the ph of these fluids likely reflects reaction with rocks that were previously altered by highly acidic magmatic fluids to an advanced argillic alteration assemblage containing quartz illite pyrophyllite anhydrite alunite in hydrothermal upflow zones fluids that do not react with advanced argillic alteration assemblages during upflow have measured ph25 c values between 3 and 4