a multivariate mixing model for identifying sediment source from magnetic measurements a sequential method for quantitative identification of sediment source components based on magnetic measurements has been developed and tested for sediments from the rhode river maryland simulated mixing tests and multiple regression were employed to establish numerical relationships between source component proportions and the magnetic measurements of mixtures on the basis of these multivariate mixing models source components of three estuarine sediment cores were estimated by linear programming the results strongly support the previous studies on this catchment which indicated a dramatic change in sediment source some 150 to 200 yr ago quantitative calculations are more useful and informative than purely qualitative descriptions

re os geochronology of the hitachi volcanogenic massive sulfide deposit the oldest ore deposit in japan the hitachi volcanogenic massive sulfide vms deposit in the hitachi belt is one of the largest cu zn sulfide deposits in japan however its primary formation age has not been precisely determined because regional and contact metamorphism have disturbed some radiometric isotope systems e g k ar ages on wall rocks further metamorphism has greatly reduced the fossil record which has limited the use of biostratigraphy to establish the ore deposit age we applied re os isotope dating to samples from two representative sulfide deposits of the greater hitachi vms deposit the fudotaki and fujimi deposits re os isotope data from the fudotaki deposit yields a model 3 age of 533 13 ma with an initial 187 os 188 os ratio of 0 35 0 20 in contrast re os isotope data from the fujimi sulfide ore did not exhibit a linear correlation suggesting that the re os isotope system there has been disturbed by regional metamorphism of higher grade than the fudotaki deposit as well as contact metamorphism during intrusion of cretaceous granitic rocks although the fudotaki sulfide ores have been metamorphosed to lower epidote amphibolite facies the well defined re os isochron allowed us to interpret the timing of primary sulfide deposition on the paleoseafloor some orebodies of the greater hitachi vms deposit have been estimated to be early carboniferous based on the scarce fossil records and considered to be distributed in the daioin formation but our results revealed that the fudotaki deposit were formed during the cambrian and occurs in the upper akazawa formation which strongly supports the idea that the cambrian beds are widely distributed in the hitachi belt and that a significant unconformity exists between the cambrian and early carboniferous above the fudotaki deposit the cambrian re os date classifies the hitachi vms deposit as the oldest dated ore deposit in japan and in turn provides an insight to understand the geologic framework and genesis of the proto japanese islands and the east asian region

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

geology and tectonics of japanese islands a review the key to understanding the geology of asia abstract the age of the major geological units in japan ranges from cambrian to quaternary precambrian basement is however expected as the provenance of by detrital clasts of conglomerate detrital zircons of metamorphic and sedimentary rocks and as metamorphic rocks intruded by 500 ma granites although rocks of paleozoic age are not widely distributed rocks and formations of late mesozoic to cenozoic can be found easily throughout japan rocks of jurassic age occur mainly in the jurassic accretionary complexes which comprise the backbone of the japanese archipelago the western part of japan is composed mainly of cretaceous to paleogene felsic volcanic and plutonic rocks and accretionary complexes the eastern part of the country is covered extensively by neogene sedimentary and volcanic rocks during the quaternary volcanoes erupted in various parts of japan and alluvial plains were formed along the coastlines of the japanese islands these geological units are divided by age and origin i e paleozoic continental margin paleozoic island arc paleozoic accretionary complexes mesozoic to paleogene accretionary complexes and cenozoic island arcs these are further subdivided into the following tectonic units e g hida oki unazuki hida gaien higo hitachi kurosegawa south kitakami nagato renge nedamo akiyoshi ultra tamba suo maizuru mino tamba chichibu chizu ryoke sanbagawa and shimanto belts the geological history of japan commenced with the breakup of the rodinia super continent at about 750 ma at about 500 ma the paleo pacific oceanic plate began to be subducted beneath the continental margin of the south china block since then proto japan has been located on the convergent margin of east asia for about 500 ma in this tectonic setting the most significant tectonic events recorded in the geology of japan are subduction accretion paired metamorphism arc volcanism back arc spreading and arc arc collision the major accretionary complexes in the japanese islands are of permian jurassic and cretaceous paleogene age these accretionary complexes became altered locally to low temperature and high pressure metamorphic or high temperature and low pressure metamorphic rocks medium pressure metamorphic rocks are limited to the unazuki and higo belts major plutonism occurred in paleozoic mesozoic and cenozoic time early paleozoic cambrian igneous activity is recorded as granites in the south kitakami belt late paleozoic igneous activity is recognized in the hida belt during cretaceous to paleogene time extensive igneous activity occurred in japan the youngest granite in japan is the takidani granite intruded at about 1 2 ma during cenozoic time the most important geologic events are back arc opening and arc arc collision the major back arc basins are the sea of japan and the shikoku and chishima basins arc arc collision occurred between the honshu and izu bonin arcs and the honshu and chishima arcs

mudflat distal fan and shallow lake sedimentation upper vallesian turolian in the tianshui basin central china evidence against the late miocene eolian loess the tianshui basin in central china contains a thick sedimentary sequence 1400 m of continental deposits aragonian to villafranchian miocene pliocene in age intense himalayan movements around the paleogene miocene boundary triggered the uplift of mountain ranges around the tianshui basin providing the deposition site for continental sediments the sedimentary infill of the basin consists of four stratigraphic units i to iv this paper focuses on unit ii most of the accommodation space was occupied by unit i so during the sedimentation of unit ii the morphology of the basin was relatively flat promoting the development of wide distal fan mudflat areas and wide shallow lakes deposits include red mudstones pedogenic and groundwater calcretes reworked calcrete deposits sheet floods fluvial channels rippled sandstones siltstones ooidal peloidal packstones palustrine limestones bioturbated marls and intraclastic limestones marls the characteristics and organization of the deposits indicate the gradual transition from alluvial to lake environments within the distal fan mudflat the deposition of reworked calcrete clasts as one of the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and red clays at the lake margins the presence of ooids and palustrine limestones suggests the possibility of ramplike margins within different energy settings the origin of some of the deposits of the basin s qa i section is under discussion and their consideration as eolian has been recently proposed however we believe this possibility is precluded by the characteristics of the deposits our proposal has important implications for revising the interpretation of miocene paleoclimatic conditions in central asia

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

rock magnetism and geochemistry of two plio pleistocene chinese loess palaeosol sequences implications for quantitative palaeoprecipitation reconstruction abstract stratigraphic and spatial variations in the magnetic properties of chinese loess are widely accepted as reflecting changes in the intensity of soil forming processes over time and space recently several workers have used statistical correlations between the magnetic susceptibility and related parameters of modern loess plateau soils and modern climate to generate transfer functions to reconstruct past temporal and spatial trends in precipitation here we try to assess the viability of this approach by conducting magnetic and geochemical measurements of two long 2 5 my loess palaeosol sequences from different locations on the modern precipitation gradient across the loess plateau one site duanjiapo is located on the southern humid margin of the plateau and the other site luochuan is located in a drier modern environment some 160 km further north our results indicate discrepancies between magnetic and geochemical indicators of weathering and soil forming intensity and that any attempt to predict palaeoprecipitation at duanjiapo using published approaches would be significantly in error overall our results indicate a complex response of magnetic mineral transformations to climate including the production of both ferrimagnetic and antiferromagnetic minerals within the same climatic interval together with the destruction of magnetic material within some of the palaeosols therefore we suggest considerable caution should be exercised in generating quantitative climatic reconstructions from a single magnetic parameter

links between bulk sediment particle size and magnetic grain size general observations and implications for chinese loess studies using a combination of particle size analysis magnetic measurements scanning electron microscopy and transmission electron microscopy imaging this study shows that in a wide range of depositional environments there is a strong link between particle size classes and magnetic response especially below the upper limit of stable single domain magnetic behaviour ferrimagnetic grain assemblages dominated by stable single domain magnetosomes regularly have peak susceptibility and remanence values in coarser grades than do those containing finer grained viscous and superparamagnetic secondary magnetic minerals formed during pedogenesis this effect is despite the fact that there is a one to two orders of magnitude size difference between the particle size boundaries at 1 or 2 m and key domain state transitions mostly below 0 05 m the implications of these results are explored using samples spanning 22 myr of loess accumulation on the chinese loess plateau the results from the loess sections complemented by data from low temperature magnetic experiments show that there are subtle distinctions in mean ferrimagnetic grain size between the pleistocene and miocene parts of the record thus allowing more refined rock magnetic interpretations of the fine grained ferrimagnetic mineral assemblages arising from the effects of weathering pedogenesis and possibly diagenesis in the sections studied

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

the record of changing hematite and goethite accumulation over the past 22 myr on the chinese loess plateau from magnetic measurements and diffuse reflectance spectroscopy 1 high field isothermal remanence hirm and diffuse reflectance spectroscopy drs wereusedto characterize hematite and goethite in a suite of bulkand particle sized fractioned samples from the chinese loess plateau representing the main changes in magnetic mineralogy over the past 22 myr the record of drs defined hematite largely reflects variations in the pedogenic fraction 8 mm makes the main contribution to goethite concentrations in the bulk samples pedogenic goethite concentrations generally vary inversely with those of hematite the lack of consistent correlations between hirm inferred mineral content and drs measurements casts doubt on the validity of using hirm to characterize the concentrations and relative proportions of hematite and goethite in sediments representing a long time span or a wide grain size distribution the progressive decline in the coercivity of the antiferromagnetic minerals in bulk samples throughout the whole period is mainly an expression of changes in the detrital fraction reflecting changes in the source region possibly involving increased aluminum substitution the good correlation between drs defined hematite and frequency dependent magnetic susceptibility in several chronologically defined subgroups of samples is consistent with the hypothesis that maghemite forms a transitional phase in a weathering sequence from ferrihydrite to hematite the results shed new light on using hirm to characterize hematite and goethite in sediments and on the history of weathering and climate change over the past 22 myr in the dust source regions and on the loess plateau

biomarkers challenge early miocene loess and inferred asian desertification 1 fine grained miocene sediments from tianshui basin northeastern tibetan plateau have received intense attention recently because these sediments were identified as loess the presence of early miocene loess pushes the timing of initiation of inland asian desertification from 8 ma back to 22 ma however mudflat distal fan and shallow lake sediments of miocene have also been reported in tianshui basin consequently the origin of these fine grained miocene sediments in this area remains controversial here we investigate then alkane biomarker characteristics of neogene sediments from a north south transect of exposures within tianshui basin and compare these molecular distributions with those published quaternary loess to help resolve the disputed origin we found thatn c23 and n c25 alkanes sourced from either aquatic macrophytes or palustrine plants are ubiquitous in the miocene sediments from tianshui basin but are largely absent in quaternary loess this striking difference between n alkane distributions in the tianshui samples and the quaternary loess casts doubt on an eolian origin for the tianshui samples and challenges the hypothesis of an early miocene onset of asian interior desertification

temperature dependence of sulfide and sulfate solubility in olivine saturated basaltic magmas abstract the sulfur concentration at pyrrhotite and anhydrite saturation in primitive hydrous basaltic melt of the 2001 2002 eruption of mt etna was determined at 200 mpa t 1050 1250 c and at log fo2 from fmq to fmq 2 2 fmq is fayalite magnetite quartz oxygen buffer at 1050 c au sample containers were used a double capsule technique using a single crystal olivine sample container closed with an olivine piston embedded in a sealed au80pd20 capsule was developed to perform experiments in s bearing hydrous basaltic systems at t 1050 c pyrrhotite is found to be a stable phase coexisting with melt at fmq fmq 0 3 whereas anhydrite is stable at fmq 1 4 fmq 2 2 the s concentration in the melt increases almost linearly from 0 12 0 01 to 0 39 0 02 wt s at fes saturation and from 0 74 0 01 to 1 08 0 04 wt s at anhydrite saturation with t ranging from 1050 1250 c the relationships between s concentration at pyrrhotite and or anhydrite saturation mgo content of the olivine saturated melt t and log fo2 observed in this study and from previous data are used to develop an empirical model for estimating the magmatic t and fo2 from the s and mgo concentrations of h2o bearing olivine saturated basaltic melts the model can also be used to determine maximum s concentrations if fo2 and mgo content of the melt are known the application of the model to compositions of melt inclusions in olivines from mt etna indicates that the most primitive magmas trapped in inclusions might have been stored at log fo2 slightly higher than fmq 1 and at t 1100 1150 c whereas more evolved melts could have been trapped at t 1100 c these values are in a good agreement with the estimates obtained by other independent methods reported in the literature

anhydrite solubility in differentiated arc magmas abstract the solubility of anhydrite in differentiated arc magmas was experimentally studied at 200 mpa and 800 1000 c over a range of oxygen fugacities from 0 5 log units above the ni nio buffer to the hematite magnetite buffer anhydrite is stable only at oxidizing conditions fo2 re reo2 whereas sulfides only form under reducing conditions the solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption at oxidizing conditions the solubility product of anhydrite increases with temperature nbo t and melt water content we provide a new calibration of the anhydrite solubility product ksp xcao xso3 which reproduces all available experimental data with greatly improved accuracy ln k sp anhydrite 8 95 146 5 nbo t 2 696 10 4 t k 19 72 nbo t 10 4 t k 0 409 h 2 o wt in this equation the molar fractions xcao and xso3 in the melt as well as the number of non bridging oxygen atoms per tetrahedron nbo t are calculated on an anhydrous basis h2o refers to the melt water content t is temperature in kelvin we apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 mt pinatubo dacite eruption was unusually large because only a small fraction of the sulfur was locked up in anhydrite in general high sulfur yields are expected when anhydrite solubility in the melt is high i e for somewhat depolymerized melts for rhyolitic systems most of the available sulfur will be locked up in anhydrite so that even very large eruptions may only have a small effect on global surface temperatures our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions

two stage gold mineralization of the axi epithermal au deposit western tianshan nw china evidence from re os dating s isotope and trace elements of pyrite the axi gold deposit is one of the largest epithermal deposits in northwestern china and is characterized by multistage generations of pyrite associated with gold mineralization genetic models for superjacent epithermal au and porphyry cu systems involve either contemporaneous or episodic mineralization implying different metal sources and ore forming events nine pyrite separates from disseminated ores associated with pyrite sericite quartz alteration in the axi deposit yield a re os isochron age of 350 10 ma mswd 5 1 initial 187os 188os ios 0 20 0 11 this age likely reflects a mixed contribution of two subtypes of disseminated pyrite py1 based on zoned pyrite crystals the isochron age of 353 6 ma mswd 1 6 ios 0 107 0 021 n 6 excluding samples with pyrite cores overlaps previous ages for andesite from the dahalajunshan formation ca 356 ma indicating that the early mineralization event occurred shortly after the formation of host rocks ca 353 ma pyrite from disseminated ores shows little variation of sulfur isotopic compositions 2 9 to 4 0 and has high cu co ni and v contents which favors a magmatic hydrothermal origin pyrite grains from gray quartz veins yield a younger re os isochron age of 332 8 ma mswd 0 22 n 4 vein hosted pyrite shows characteristics of a mantle derived magma source ios 0 171 0 024 34s 0 10 3 10 which result from the intrusion driven convective hydrothermal circulation accompanying fluid exsolution and metal remobilization from basement and wallrocks our data demonstrate that the axi gold deposit was formed during two temporally separated hydrothermal events this model of ore formation may apply to other epithermal porphyry deposits within the axi tawuerbieke district disseminated au and porphyry style au cu mineralization occurred shortly after magmatic activity 356 353 ma whereas epithermal style au mineralization occurred at ca 332 ma

oxygen isotope study of the kamioka zn pb skarn deposits central japan the kamioka zn pb deposits consist of clinopyroxene rich skarns replacing limestone lenses in hida gneissose rocks paleozoic metabasite early jurassic funatsu granitic rocks and late cretaceous porphyritic dikes and stocks are the known igneous rocks in the mining area oxygen isotopic compositions of eight separates each of clinopyroxene and quartz from the deposits table 1 and some minerals and rocks from the major rock units around the deposits table 2 have been analyzed the estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits range as low as 4 to 3 smow these values are considerably lower than expected from magmatic waters and demonstrate that none of the igneous rocks in the area could be a direct source of the skarn and ore forming fluids the data instead show that the deposits are formed by a huge convective circulation of solutions of meteoric water origin promoted by a hidden batholithic intrusion at the time of the late cretaceous

magnetic enhancement is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

sulfur and chlorine in late cretaceous deccan magmas and eruptive gas release large volume p hoehoe lava flows erupted 67 to 65 million years ago forming the deccan traps india the impact of these flood basalt eruptions on the global atmosphere and the coeval end cretaceous mass extinction has been uncertain to assess the potential gas release from this volcanism we measured sulfur and chlorine concentrations in rare glass inclusions inside crystals and on glassy selvages preserved within lavas concentrations range from 1400 parts per million of s and 900 parts per million of cl in inclusions down to a few hundred parts per million in the lava these data indicate that eruptions of deccan lavas could have released at most 0 103 weight of s yielding up to 5 4 teragrams of so2 per cubic kilometer of lava a more conservative estimate is 0 07 weight of s and 0 04 weight of cl yielding 3 5 teragrams of so2 and 1 teragram of hcl for every cubic kilometer of lava erupted the flows were very large in volume and these results imply that huge amounts of s and cl gases were released the environmental impact from even individual eruptions during past flood basalt activity was probably severe

genesis of chlorine and sulphur in fumarolic emissions at vulcano island italy assessment of ph and redox conditions in the hydrothermal system chlorine and sulphur bearing compounds in fumarole discharges of the la fossa crater at vulcano island italy can be modelled by a mixing process between magmatic gases and vapour from a boiling hydrothermal system this allows estimating the compounds in both endmembers magma degassing cannot explain the time variation of sulphur and hcl concentrations in the deep endmember which are more probably linked to reactions of solid phases at depth before mixing with the hydrothermal vapours based on the p t conditions and speciation of the boiling hydrothermal system below la fossa the hcl and stot contents in the hydrothermal vapours were used to compute the redox conditions and ph of the aqueous solution the results suggest that the haematite magnetite buffer controls the hydrothermal fo2 values while the ph has increased since the end of the 1970s the main processes affecting ph values may be linked to na ca exchanges between evolved seawater feeding the boiling hydrothermal system and local rocks while na is removed from water calcium enters the solution undergoes hydrolysis and produces hcl lowering the ph of the water the increasing water rock ratio within the hydrothermal system lowers the ca availability so the aqueous solution becomes less acidic seawater flowing towards the boiling hydrothermal brine dissolves a large quantity of pyrite along its path in the boiling hydrothermal system dissolved sulphur precipitates as pyrite and anhydrite and becomes partitioned in vapour phase as h2s and so2 these results are in agreement with the paragenesis of hydrothermal alteration minerals recovered in drilled wells at vulcano and are also in agreement with the isotopic composition of sulphur emitted by the crater fumaroles

formation of volcanogenic massive sulfide deposits the kuroko perspective abstract the main objective of this paper is to identify the geochemical hydrological igneous and tectonic processes that led to the variations in the physical size geometry and chemical mineralogy metal ratios and zoning characteristics of volcanogenic massive sulfide deposits with respect to space from a scale of mining district size area to a global scale and time from a all volcanogenic massive sulfide deposits vmsds appear to have formed in extensional tectonic settings such as at mid ocean spreading centers backarc spreading centers and intracontinental rifts and failed rifts all vmsds appear to have formed in submarine depressions by seawater that became ore forming fluids through interactions with the heated upper crustal rocks submarine depressions especially those created by submarine caldera formation and or by large scale tectonic activities e g rifting become most favorable sites for the formation of large vmsds because of hydrological physical and chemical reasons the fundamental processes leading to the formation of vmsds include the following six processes 1 1 intrusion of a heat source typically a 10 3 km size pluton into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton the radius of a circulation cell is typically 5 km the temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350 c and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years the majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity 2 2 reactions between low temperature t 2 4 as disseminated gypsum and anhydrite in the country rocks 3 3 reactions of the modified seawater with higher temperature rocks at depths during the waxing stage cause the transformation of the seawater to metal and h 2 s rich ore forming fluids the metals and sulfide sulfur are leached from the county rocks the previously formed gypsum and anhydrite are reduced by fe 2 bearing minerals and organic matter providing additional h 2 s the mass of high temperature rocks that provide the metals and reduced sulfur is typically 10 11 tons 40 km 3 in volume the roles of magmatic fluids or gases are minor in most massive sulfide systems except for so 2 to produce acid type alteration in some systems 4 4 reactions between the ore forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores 5 5 mixing of the ore forming fluids with local seawater within unconsolidated sediments and or on the seafloor causes precipitation of primitive ores with the black ore mineralogy sphalerite galena pyrite barite anhydrite 6 6 reactions between the primitive ores with later and hotter hydrothermal fluids cause transformation of primitive ores to matured ores that are enriched in chalcopyrite and pyrite variations in the mineralogical and elemental characteristics the geometry and the size of submarine hydrothermal deposits are controlled by the following four parameters 1 a the chemical and physical characteristics of seawater composition temperature density which depend largely on the geographical settings e g equatorial evaporating basins 2 b the chemical and physical characteristics of the plumbing system lithology fractures 3 c the thermal structure of the plumbing system which is determined largely by the ambient geothermal gradient and the size and temperature of the intrusive and 4 d the physical characteristics of the seafloor depth basin topography for example the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in pb and ba compared to those developed in felsic plumbing systems the lower temperature systems are generally poorer in sulfides but richer in iron oxides and sulfates the higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores contrasts in the metal ratios between the noranda type archean vmsds and the younger vmsds reflect the differences in the geothermal gradient of the plumbing systems the submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins the basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history from at least 3 5 billion year ago to the present

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

sulfur bearing magmatic accessory minerals almost all magmas contain sulfide or sulfate bearing phases in most natural samples the sulfur bearing phase is a sulfide which typically is pyrrhotite fe1 x s or pyrite fes2 although chalcopyrite cufes2 pentlandite fe ni 9s8 sphalerite zns or molybdenite mos2 may be present as well sulfate minerals are rare at magmatic conditions and anhydrite caso4 is the most common other magmatic so4 bearing minerals include the sodalite group minerals hauyne simplified formula na ca 4 8 al6si6 o s 24 so4 cl 1 2 scapolite minerals silvialite ca na 4al6si6o24 so4 co3 and s bearing apatite ca5 po4 3 f cl oh barite baso4 has been mentioned in rare cases marchev 1991 sulfur bearing minerals usually constitute a negligible fraction of the mineral assemblage in magmatic rocks and thus can be classified as accessory minerals the crystallization of sulfide sulfate and s bearing minerals strongly depends on melt composition temperature and pressure and the s speciation in melt which in turn is strongly dependent on the prevailing oxygen fugacity baker and moretti 2011 this volume wilke et al 2011 this volume irrespectively of the low abundance of s bearing minerals the evolution of sulfur in magmas may be evaluated from the occurrence of sulfides and sulfates these minerals are critical for estimating the activity of various sulfur bearing species in magmas and can be used to constrain the oxygen fugacity and the s concentration in the melt e g pre eruptive sulfur concentration in melts the presence of either sulfide or sulfate in silicate melt indicates that the predominant dissolved sulfur species in the melt are s2 or s6 respectively typically one of these species is dominant but there are conditions where s2

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

magnetic minerals in calcic luvisols chromic developed in a warm mediterranean region of spain origin and paleoenvironmental significance abstract soil formation under aerobic conditions usually enhances magnetic signals mainly through neoformation of sub micron magnetite and or maghemite in order to better understand the nature and magnitude of the enhancement in this work we characterized the iron fe oxides and magnetic properties of two calcic luvisols chromic developed on calcareous orthoquartzites in a spanish region with a warm mediterranean climate weathering of the fe bearing minerals in the parent material mostly fe rich smectite had resulted in the neoformation of hematite and maghemite rather than goethite thus causing a substantial increase in magnetic susceptibility saturation magnetization m s and other magnetic signals the absolute frequency dependent magnetic susceptibility fd which is a typical proxy for the concentration of sub micron superparamagnetic pedogenic maghemite was strongly correlated with the concentration of hematite hm the estimated percent frequency dependent magnetic susceptibility fd was 15 7 this and various other magnetic indicators indicate that the grain size distribution gsd of the pedogenic maghemite is narrower around the superparamagnetic single domain threshold than is that of maghemite in soils and paleosols developed under other temperate climates e g the chinese loesss plateau where fd fd ratio fd the hematite goethite ratio and several indicators of the degree of weathering provides a better tool for paleoclimatic reconstructions than does the current use of alone

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

melt inclusion record of the conditions of ascent degassing and extrusion of volatile rich alkali basalt during the powerful 2002 flank eruption of mount etna italy 1 two unusual highly explosive flank eruptions succeeded on mount etna in july august 2001 and in october 2002 to january 2003 raising the possibility of changing magmatic conditions here we decipher the origin and mechanisms of the second eruption from the composition and volatile h2o co2 s cl content of olivine hosted melt inclusions in explosive products from its south flank vents our results demonstrate that powerful lava fountains and ash columns at the eruption onset were sustained by closed system ascent of a batch of primitive volatile rich 4 wt basaltic magma that rose from 10 km depth below sea level bsl and suddenly extruded through 2001 fractures maintained opened by eastward flank spreading this magma the most primitive for 240 years probably represents the alkali rich parental end member responsible for etna lavas evolution since the early 1970s few of it was directly extruded at the eruption onset but its input likely pressurized the shallow plumbing system several weeks before the eruption this latter was subsequently fed by the extrusion and degassing of larger amounts of the same but slightly more evolved magma that were ponding at 6 4 km bsl in agreement with seismic data and with the lack of preeruptive so2 accumulation above the initial depth of sulphur exsolution 3 km bsl we find that while ponding this magma was flushed and dehydrated by a co2 rich gas phase of deeper derivation a process that may commonly affect the plumbing system of etna and other alkali basaltic volcanoes

environmental magnetism a practical guide j walden f oldfield j and smith eds technical guide no 6 quaternary research association london 1999 243 pp price 17 00 9 00 to qra members isbn 0 907780 42 3

the magnetic properties of loess and paleosol samples from the chinese loess plateau spanning the last 22 million years abstract magnetic measurements susceptibility isothermal and anhysteretic remanence and quotients derived from these are presented for a suite of loess and paleosol samples from sites on the chinese loess plateau the three sites xifeng dongwan and qinan qa i together span most of the last 22 million years the results provide the first multi parameter magnetic measurements from pre pleistocene loess paleosol sequences that began accumulation in the early miocene mass specific measurements have been corrected for carbonate concentrations which peak in the loess layers and range up to 57 all the magnetic properties recorded indicate variability on both orbital and supra orbital timescales the changing magnetic properties allow the record to be divided into a sequence of eight sample groups that broadly parallel the main supra orbital changes in magnetic susceptibility the pre pleistocene parts of the record include intervals mainly late miocene and pliocene during which loess as well as paleosol layers are characterized by high values for properties such as frequency dependent susceptibility fd usually associated with strong weathering most of the miocene record prior to 8 5 ma with the exception of a brief interval from ca 14 4 to 15 9 ma shows reduced values for indicators of pedogenic ferrimagnetic concentrations in both the loess and paleosol layers as well as a low amplitude of variability between loess and paleosol values the palaeoenvironmental implications of this part of the sequence are unclear since they hinge on the type of model of pedogenic magnetic mineral formation adopted high field remanence measurements indicate that the coercivity of the antiferromagnetic minerals represented declined progressively throughout the whole period in both the loess and the paleosol samples though there is no unambiguous evidence for long term diagenetic alteration of the magnetic properties on timescales beyond the orbital ones that drive the loess paleosol alternations the present results suggest caution in applying existing climofunctions based on magnetic susceptibility to deposits spanning the whole of the last 22 ma

early diagenesis in north atlantic abyssal plain sediments characterized by rock magnetic and geochemical indices processes of early diagenesis are investigated in a sequence of late quaternary turbiditic sediments from the madeira abyssal plain map west of the nw african continental margin in three sediment cores from this region solid phase geochemical indices of redox sensitive ion mobilization are compared with rock magnetic parameters as proxies for diagenesis characterization the mud dominated distal turbidites are emplaced mainly as a result of glacio eustatic changes in sea level and derive both from different sites on the nw african margin and from the flanks of the canary islands thus the turbidites are of variable composition especially in terms of carbonate detrital magnetic mineral and organic carbon content within organic rich 0 5 corg turbidite horizons remineralization of organic detritus proceeds in two stages the initial stage involves suboxic reductive diagenesis following depletion of pore water o2 while the later stage involves oxidative diagenesis associated with the slow descent of an oxidation front through the sediment due to diffusion of o2 from the overlying seawater rock magnetic parameters of these sediments when expressed on a carbonate free basis reveal that significant depletion of detrital ferrimagnetic iron fe2 fe3 oxide grains has occurred within the organic rich turbidites during suboxic diagenesis normalized quotients of magnetic parameters and remanence coercivity profiles of selected samples also show that reductive diagenesis is a ferrimagnetic grain size selective process but it has a minimal effect on the canted antiferromagnetic fe3 oxides in the sediment such components if present therefore become relatively enriched in magnetic assemblages as the ferrimagnetic grains are progressively dissolved in all three cores studied however there is clear evidence for the presence of ultrafine ferrimagnetic iron oxide grains at depth within the suboxic zones of organic rich turbidites beneath both active and fossil oxidation fronts these grains are probably associated with populations of live magnetotactic bacteria which inhabit such organic rich horizons and which form a link in the chain of bacterially mediated reactions normally associated with suboxic diagenesis these results comply with previous observations made in studies of suboxic diagenesis in hemipelagic sediments and demonstrate the value of rapid and non destructive rock magnetic measurements for illuminating redoxomorphic processes of diagenesis involving transformation of iron phases in deep sea sediments

quantifying grain size distribution of pedogenic magnetic particles in chinese loess and its significance for pedogenesis quaternary glacial interglacial cycles have been imprinted on the chinese loess paleosol sequences through pedogenesis in order to accurately decode the paleoclimatic signals carried by these pedogenic particles it is essential to quantify the pedogenically produced magnetic particles in terms of mineralogy as well as grain size distribution gsd to date the gsd has not been accurately determined because of the dearth of available means for analyzing extremely fine grained nanometer scale pedogenic magnetic particles using low temperature techniques we systematically investigated the temperature dependency of fd defined as 1hz 10hz where 1hz and 10hz are ac magnetic susceptibility measured at 1 and 10 hz respectively from two characteristic loess profiles one located at the western chinese loess plateau and the other in the central plateau on the basis of neel theory for a shape anisotropy dominant grain and experimental analysis at low temperatures a quantitative gsd for pedogenic particles in chinese loess paleosols was constructed we found that the dominant magnetic grain size lies just above the superparamagnetic single domain threshold 20 25 nm and that the gsd is almost independent of the degree of pedogenesis this observation agrees well with other constraints from previous studies this new gsd model improves our understanding of the pedogenic processes in chinese loess enabling further explicit linkage of environmental magnetism to paleoclimate changes

magnetostratigraphy of a late miocene pliocene loess soil sequence in the western loess plateau in china 1 eolian deposits of pliocene age have never been reported from the western loess plateau in china here a 73 7 m eolian sequence is dated using magnetostratigraphic method and micromammalian fossils the polarity zonation correlates with the geomagnetic polarity timescale gpts from chron 3br 1r to chron 2an 3n indicating an age from 7 10 to 3 52 ma bp the sequence is characterized by clear expression of eighty four pairs of loess and soil layers while individual soils are basically indefinable for the eolian deposits of the same age in the eastern loess plateau suggesting that the later has experienced other geological processes this sequence extends the upper limit of the previously reported miocene loess soil sequences at qinan into the pliocene about 3 52 ma bp

petrography mineral chemistry fluid inclusion microthermometry and re os geochronology of the kure volcanogenic massive sulfide deposit central pontides northern turkey the re os isotopic system is applied for the first time to the sulfide ores and the overlying black shales at the kure volcanogenic massive sulfide deposit of the central pontides northern turkey the ore samples collected include predominantly pyrite accompanied by chalcopyrite sphalerite and other species massive ore is almost free of gangues whereas the stockwork ore includes quartz and calcite gangue the composition of sphalerite is similar to ancient and modern massive sulfide mineralizations globally microthermometric studies from quartz from the stockwork ore has shown two populations of two phase fluid inclusions with vapor liquid ratios between 4 to 28 low to intermediate th 161 5 317 0 c and low salinities 0 9 5 wt nacl equiv which are mostly in good agreement with the ranges for volcanogenic massive sulfide mineralizations these studies also suggest a h2o cacl2 kcl mgcl2 ore forming fluid system in a shallower subsurface near the seafloor vents the re os dating of the llhr sulfides yield a nominal depositional age of upper toarcian for the massive sulfide mineralization two largely different model ages obtained are attributed to other pyrite crystallization events prior to and postdating the main sulfide deposition some lower homogenization temperatures 200 c from the quartz of the stockwork may also similarly be related to the post vms events it is concluded that a submarine volcanic extrusion episode has continued until upper toarcian in the kure basin when it has entered a stagnation period that allowed the discharge of hydrothermally circulated sulfide laden fluids from the seafloor vents this age data promotes the palaeotectonic models interpreting the kure basin as a permian early jurassic marginal back arc basin of the devonian triassic karakaya ocean the re os data from the overlying black shale provide a glimpse to the initial os isotope ratio of the water column at the time of the sedimentation 0 45 0 46 for 180 ma the lack of common os from the sulfides does not let us to infer a source of os and initial 187os 188os ratios from the black shale are not statistically robust to make a significant deduction a further detailed study on the isotopic composition of the black shale strata may help us to make an apporach to the os source s in the deposition environment of the kure vms deposit

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

major and trace element geochemistry and os isotopic composition of metalliferous umbers from the late cretaceous japanese accretionary complex 1 metalliferous umbers and red shales occur as unique products of the kula pacific ridge forearc collision in the late cretaceous shimanto supergroup an accretionary complex in japan these umbers are closely associated with greenstones of mid ocean ridge basalt morb origin and are regarded as hydrothermal metalliferous precipitates related to mor type volcanism the umbers and red shales were deposited in the trench area where both terrigenous detritus from land and hydrothermal metalliferous particulates from a mor were supplied simultaneously besides a predominance of fe and mn the umbers exhibit remarkable enrichments in p v co ni zn y mo rare earth elements rees and os relative to continental crustal abundances the x fe x mn p v co ni zn y and rees ratios and paas normalized ree patterns of the umbers are very similar to those of modern hydrothermal plume fallout precipitates deposited on flanks of mor this indicates that the umbers preserve primary geochemical signatures of hydrothermal metalliferous sediments that scavenged seawater derived elements and thus can be used as a proxy for late cretaceous seawater the marine 187os 188os ratios reconstructed from the late maastrichtian umbers range from 0 42 to 0 56 and are very consistent with recent data obtained from the pacific and atlantic pelagic carbonates that record an abrupt decline from 0 55 to 0 4 during the period between 67 0 ma and 65 7 ma

wind blown origin of dongwan late miocene pliocene dust sequence documented by land snail record in western chinese loess plateau recently the first late miocene pliocene eolian deposits from the western chinese loess plateau have been reported these deposits would complement the eolian record between quaternary loess paleosol sequences and miocene loess sequences if their wind blown origin could be documented however although several lines of evidence indicate the eolian origin of this sequence it is still necessary to address this issue through further efforts among these biological approaches are of particular value here we analyze the composition and preservation conditions of mollusk assemblages in the dongwan section our results show that all mollusk fossil individuals are preserved in perfect condition without indicating any reworking all identifiable mollusk species are terrestrial and are mostly identical to those identified in the quaternary loess paleosol sequences of the chi nese loess plateau generally the cold aridiphilous species are dominant in the loess layers while thermo humidiphilous species are mostly encountered in the paleosols the close similarity of the mollusk record in both the dongwan late miocene pliocene deposits and the quaternary loess sequence in the chinese loess plateau supports the supposition that the dongwan section is a typical loess paleosol sequence and is without any doubt of wind blown origin

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

magnetostratigraphy of an early middle miocene loess soil sequence in the western loess plateau of china 1 stratigraphy and magnetic susceptibility of the quaternary eolian deposits at different sites in china can be closely correlated confirming their spatial coherence and temporal continuity the extent to which these conclusions are true for the miocene loess soil sequences remains to be addressed here a 231 9 m eolian section qa iii is geomagnetically dated yielding an age span of 21 4 11 4 ma with the portion older than 19 6 ma being partially water reworked the magnetozones litholigic structure and magnetic susceptibility of the sequence are highly correlative with the qa i and qa ii sections 30 km west of qa iii these sequences demonstrate that the miocene loess deposits are also spatially correlative in stratigraphy present a near continuous sequence of paleoenvironment changes and that magnetic susceptibility is a useful tool for stratigraphic correlation the basal age of qa iii confirms again the onset of asian inland deserts and monsoon dominate climates by the early miocene

modeling the solubility of sulfur in magmas a 50 year old geochemical challenge there are myriad reasons why we wish to understand the behavior of sulfur in magmatic systems reasons that vary from pure intellectual curiosity to possible impacts on society and its resources since ancient times sulfur has been associated with volcanic activity and the role of sulfur in the formation of ore deposits has long been recognized because of the necessity of metal ores for our modern life style e g barnes 1979 naldrett 1989 simon and ripley 2011 this volume recently the mechanisms and quantities of sulfur freed from natural magmas have become an important environmental issue due to their potential effects on global climate change for example the average annual volcanic so2 emission rate of 7 5 to 10 5 teragrams tg per year halmer et al 2002 may contribute 10 of the global atmospheric sulfur input halmer et al 2002 smith et al 2004 and individual eruptive episodes can rapidly contribute gigantic sulfur loads to the atmosphere 100 s to 1000 s of tg depending on the scale of the eruption self 2006 such sulfur emissions can produce potentially catastrophic local and global changes e g fedele et al 2003 ward 2009 courtillot and rennes 2003 correlated the timing of flood basalts with extinction events in earth s history and hypothesized a causal relation part of the kill mechanism responsible for extinction may be volcanically derived sulfur creating anoxic oceans and another part of the mechanism may be climatic changes brought about by sulfur injection into the atmosphere ward 2009 indeed erwin 2006 advocates that sulfur released from the eruption of the siberian flood basalts played a role in the end permian extinction in light of the evidence that volcanic degassing is a significant source of sulfur to the atmosphere stoiber et al 1987 symonds et al 1994 andres

re os geochronology of the iimori besshi type massive sulfide deposit in the sanbagawa metamorphic belt japan abstract besshi type cu deposits are strata bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents although there are numerous besshi type deposits in the sanbagawa metamorphic belt japan their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints we report re os data for the iimori deposit one of the largest besshi type deposits in western kii peninsula in order to examine the robustness of the re os isotope system for dating sulfide minerals in the high p t metamorphic belt and to elucidate the primary depositional environment of the iimori sulfide ores an 11 point re os isochron plot yields an age of 156 8 3 6 ma as this re os isochron age is significantly older than the timing of the sanbagawa peak metamorphism 110 120 or 90 ma and a well defined isochron was obtained the re os age determined here is most likely the primary depositional age despite high grade metamorphism at up to 520 25 c and 8 9 5 kbar the re os isotope system of the iimori sulfides was not disturbed hence we consider that the whole rock re os closure temperature for the iimori sulfide ores was probably higher than 500 c as the accretion age of the sanbagawa metamorphic belt is considered to be 120 130 or 65 90 ma on the basis of radiolarian and radiometric ages we estimated the time from the iimori sulfide deposition on the paleo seafloor to its accretion at the convergent plate boundary to be greater than 25 myr consequently the depositional environment of the iimori sulfide ores was not in the marginal sea but was truly pelagic

2001 flank eruption of the alkali and volatile rich primitive basalt responsible for mount etna s evolution in the last three decades abstract since the early 1970s enhanced eruptive activity of mount etna has been accompanied by selective geochemical changes in erupted lavas among which a gradual increase of alkalis whose origin is still debated here we provide further insight into the origin of this recent evolution based on a detailed study of the chemistry and dissolved volatile content of melt inclusions trapped in olivine crystals of unusual plagioclase poor primitive basalt that was extruded during a highly explosive flank eruption in july august 2001 two types of lava were erupted simultaneously along a n s fracture system trachybasalts from the upper vents 2950 2700 m were simply drained out by fracturing of the central volcanic conduit they are identical to summit crater lavas and contain mg poor olivines fo 70 72 with evolved and volatile poor melt inclusions that represent late stage crystallisation during shallow open conduit degassing in contrast plagioclase poor basalt 80 of total extruded through the lower vents 2550 2100 m derived from lateral dyke intrusion of a more primitive and volatile rich magma across the sedimentary basement this primitive melt is best preserved in rare fo 82 4 80 5 skeletal olivines present in lapilli deposits from the most powerful activities at the 2550 m vent its high dissolved contents of h 2 o 3 4 wt co 2 0 11 to 0 41 wt s 0 32 wt cl 0 16 wt and f 0 094 wt point to its closed system ascent from 400 to 250 mpa 12 to 6 5 km depth b s l however the predominance of euhedral olivine phenocrysts with common reverse zoning cores fo 76 78 and rims fo 78 80 and decrepited inclusions shows that most of the erupted basalt derived from a slightly more evolved crystallizing body of the same magma that was invaded by the uprising primitive melt prior to erupting the few preserved inclusions in these olivines indicate pre eruptive storage of that magma body at about 5 km depth b s l in coherence with seismic data we propose that the 2001 flank eruption resulted from gradual overpressuring of etna s shallow plumbing system due to the influx of volatile rich primitive basalt that may have begun several months in advance we find that this basalt is much richer in alkalis 2 0 wt k 2 o and has higher s cl 2 0 but lower cl k and cl f ratios than all pre 1970s etnean lavas 1 4 wt k 2 o s cl 1 5 as further exemplified by melt inclusions in entrained olivine xenocrysts combining these new observations with previously published data we argue that the 2001 basalt represents a new alkali rich basic end member feeding mt etna only few amount of which had previously been extruded during a 1974 peripheral eruption and more recently during brief paroxysmal summit events over the last three decades this new magma has progressively mixed with and replaced the former k poorer trachybasalts filling the plumbing system leading to extrusion of gradually more primitive and alkali richer lavas its geochemical singularities cannot result from shallow crustal contaminations instead they suggest the involvement of an alkali richer but cl poorer arc type component during recent magma genesis beneath etna

rock magnetic properties confirm the eolian origin of miocene sequences from the west of the chinese loess plateau abstract diagnostic rock magnetic characteristics of miocene sequences from the western part of the chinese loess plateau are used to confirm the eolian nature of sections the origin of which has been a matter of recent dispute alonso zarza et al 2009 2010 guo et al 2010 the key magnetic properties include i detailed correlation of both the orbitally timed and supra orbital variations in magnetic properties between widely separated sections ii the bi modal distribution of magnetic properties with respect to particle size reflecting in situ neoformation alongside the deposition of detrital minerals derived from the source areas iii the consistent presence in the clay fractions of fine ferrimagnetic grains close to the superparamagnetic stable single domain transition all within the size range characteristic of those formed by weathering and pedogenesis under at least partially aerobic conditions and iv absence of evidence for lacustrine indicators such as bacterial magnetosome assemblages sub oxic diagenesis or greigite formation

particle size separation and evidence for pedogenesis in samples from the chinese loess plateau spanning the past 22 m y a comparison between particle size distributions determined by laser diffraction and the pipette method confi rms previous studies that point to a variable underestimate of the clay fraction using laser diffraction relative to the values obtained by pipette analysis in order to yield four particle sized fractions 8 m for further analysis the pipette method was used on loess and paleosol samples from sites on the chinese loess plateau spanning the past 22 m y in all cases a subsidiary mode in the 8 m fraction provides a basis for evaluating the relative contributions of pedogenic and detrital components pretreatment using acetic rather than hydrochloric acid for carbonate removal results in no signifi cant loss of ferrimagnetic minerals and allows magnetic characterization of the separate fractions this confi rms the isolation of almost all the fi nest pedogenic ferrimagnetic grains in the clay fraction and their negligible contribution to the magnetic properties of the coarse fractions in all the samples from early miocene time onward because similar conclusions may be drawn from previous studies of late pleistocene samples from the east central and extreme western parts of the chinese loess plateau we conclude that this approach provides a basis for separately characterizing eolian deposition and pedogenesis throughout the region and for the whole time span of loess accumulation

establishing fire incidence in temperate soils using magnetic measurements abstract natural unburnt topsoil samples from the cotswolds region of england and samples from archaeological contexts in the uk and hungary some of which are known to have been affected by burning have been used to identify a distinctive magnetic signature linked to the effects of fire on magnetic properties a combination of bulk low field lf and frequency dependent fd magnetic susceptibility and normalized anhysteretic remanent magnetization arm measurements have been used on both unburnt and experimentally burnt samples from the cotswolds and on the archaeological samples complementary determinations were made for both sets of samples of the maximum potential susceptibility max and hence percentage fractional conversion conv which provides independent evidence of burning the results show that the ferrimagnetic mineral assemblages produced as a result of fire have a significantly finer grain size than those arising from weathering and soil formation alone burning thus gives rise to a distinctive envelope of values on a bilogarithmic plot of arm fd versus arm lf such a diagram provides a convenient basis for identifying magnetic signatures in soils archaeological materials and palaeosols that have arisen mainly through burning

reos dating of molybdenites from ore deposits in japan implication for the closure temperature of the reos system for molybdenite and the cooling history of molybdenum ore deposits abstract rhenium and osmium abundances were determined on molybdenites from eighteen ore deposits in japan fifteen vein type a skarn type a greisen type and a pegmatite type deposit re os ages obtained for molybdenites from northeastern central and southwestern japan are 100 130 ma 50 75 ma and ca 10 ma respectively reflecting the ages of regional igneous activities in individual areas for vein type ore deposits re os ages for molybdenites agree with rb sr whole rock ages of host granitoids while they are 3 12 ma older than k ar mineral ages of the host rocks on the other hand re os ages of molybdenites from skarn pegmatite and greisen type ore deposits agree with k ar ages of the host rocks the comparison of re os ages for molybdenites with rb sr and k ar ages of host rocks in vein type deposits suggests that re os closure temperature for vein molybdenite is close to whole rock rb sr closure temperature for host granitic rocks i e roughly estimated to be around 500 c and higher than k ar closure temperature for host granodiorites i e 230 370 c if the thermal history of vein molybdenites is essentially equivalent to that of host rocks one possible explanation for age discrepancies of 3 12 ma between re os ages for molybdenites and k ar ages for the wall rocks observed in vein type molybdenum deposits is that later thermal events after formation of molybdenum ores may reset k ar ages hydrothermal alteration might have occurred in such a temperature condition as to disturb k ar mineral systems in wall rocks and made them younger but not the re os system in molybdenite the other explanation might be that the age discrepancies correspond to a cooling interval from ca 500 to 300 c of host granitoid on the other hand the agreement of re os ages of molybdenites and k ar ages of host rocks in skarn pegmatite and greisen type deposits in this study indicates no later disturbance for k ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits

correlation of himalayan exhumation rates and asian monsoon intensity although most data suggest that the india eurasia continental collision began 45 55 myr ago the architecture of the himalayan tibetan orogen is dominated by deformational structures developed in the neogene period 23 myr ago the stratigraphic record and thermochronometric data indicate that erosion of the himalaya intensified as this constructional phase began and reached a peak around 15 myr ago it remained high until 10 5 myr ago and subsequently slowed gradually to 3 5 myr ago but then began to increase once again in the late pliocene and pleistocene epochs here we present weathering records from the south china sea bay of bengal and arabian sea that permit asian monsoon climate to be reconstructed back to the earliest neogene these indicate a correlation between the rate of himalayan exhumation as inferred from published thermochronometric data and monsoon intensity over the past 23 myr we interpret this correlation as indicating dynamic coupling between neogene climate and both erosion and deformation in the himalaya although the india eurasia collision initiated 50 myr ago major deformation and exhumation of the himalaya did not begin until the early neogene 23 myr ago this coincides with the increased intensity of the asian monsoons as indicated by weathering records from the south china sea bay of bengal and arabian sea and hints at a dynamic coupling between climate and both erosion and deformation in the himalaya

sources of fine grained magnetic minerals in sediments a problem revisited progress in the discrimination of fine grained magnetic minerals in sediments and sediment sources using measurements of magnetic susceptibility at two frequencies and of magnetic remanence generated by a combination of direct and alternating currents is summarized the former measurements yield values for low field and frequency dependent susceptibility lf and fd respectively the latter generate an anhysteretic remanent magnetisation arm that when normalized to the dc bias field can be represented as the susceptibility of arm arm using quotients derived from lf fd and arm to generate bi logarithmic plots it is possible to discriminate between assemblages dominated by magnetic minerals formed through pedogenesis and those arising from the presence of magnetotactic bacteria that use chains of magnetic particles to seek optimum environments in surface sediments sediments to which both types of magnetic mineral contribute occupy positions between the envelopes of values typical of soil d

constraints on the genesis of gold mineralization at the homestake gold deposit black hills south dakota from rhenium osmium sulfide geochronology the homestake gold deposit located in the black hills south dakota usa is one of the largest known hydrothermal gold deposits globally with total mining production exceeding 40 moz au rhenium osmium geochronology of ore associated arsenopyrite and pyrrhotite was performed in an effort to delineate the timing of gold mineralization in relation to known tectonothermal events in the northern black hills arsenopyrite yields a rhenium osmium re os age of 1 736 8 ma mean squared weighted deviation 1 6 consistent with existing age constraints for gold mineralization whereas re os pyrrhotite data are highly scattered and do not yield a meaningful mineralization age this is taken to indicate that the re os arsenopyrite chronometer is robust to at least 400 c whereas the re os pyrrhotite chronometer is likely disturbed by temperatures of 300 350 c the re os arsenopyrite age and initial os ratio 0 28 0 15 are interpreted to indicate that gold was introduced at ca 1 730 ma coincident with the onset of exhumation of crustal blocks and possibly the earliest intrusive phases of harney peak granite magmatism new in situ u pb monazite analyses from an aplite dike in the east central black hills indicate that granite magmatism was a protracted event persisting until at least ca 1 690 ma

melt inclusion investigation of the volatile behaviour in historic alkali basaltic magmas of etna crystallization paths of basaltic 1763 eruption and hawaiitic 1865 and 1329 eruptions scoria from etna were deduced from mineralogy and melt inclusion chemistry the volatile behaviour was investigated through the study of melt inclusions trapped in the phenocrysts and those of the whole rocks and the matrix glasses the results from the 1763 eruption point to the early crystallization of olivine fo 81 7 from a water rich alkaline basalt with high cl 1750 2000 ppm and s 2100 2400 ppm concentrations the hawaiitic melt inclusions trapped in olivine fo 74 salite and plagioclase are characterized by a decrease in cl k2o and s k2o ratios in each investigated system there is good correlation between k2o and p2o5 in the whole rocks cl ranges from 980 to 1680 ppm from basaltic to hawaiitic lavas whereas s 110 136 ppm remains low cl and s behaviour in the 1763 magma suggests an early degassing stage of cl and s with co2 and a water rich gaseous phase for a pressure close to 100 mpa consistent with a permanent outgassing at the summit craters of etna during the eruption the sulphur remaining in the hawaiitic liquid is lost and the degassing of chlorine is limited such a degassing model can be extended to the 1865 and 1329a d eruptions

anhydrite an important sulfur binder limiting the climatic impact of subaerial volcanic eruptions gaseous sulfur compounds are critical climate active volatile components released by volcanoes volcanic eruptions can emit massive amounts of h 2 s and so 2 into the atmosphere which react with oxygen and h 2 o to sulfuric acid formation of h 2 so 4 aerosols which have on a geological timescale short term residence times of month or years may have global climatic impact the phase stability of sulfur bearing minerals such as anhydrite in erupting magmas may be a key controlling factor limiting so 2 emission during subaerial volcanic activity huang and keppler january 2015 issue of american mineralogist

diffusion and redox reactions of sulfur in silicate melts although large scale transport in magmas is usually controlled by convection diffusion of sulfur in silicate melts nevertheless plays a crucial role in the kinetics of various magmatic processes the most important process is probably the degassing of magmas and melts initiated by an oversaturation of the melt with respect to dissolved volatiles such oversaturation can be caused in nature i e by decompression when a magma ascends to the earth surface but the degassing of melts is also of major interest for technical applications e g during fining of melts in industrial glass production the kinetics of volcanic eruptions and the fining of glass melts are basically controlled by the dynamics of bubble nucleation and growth and these properties are strongly affected by the diffusion of volatiles from the melt into bubbles nemec 1980a b sparks et al 1994 muller simon 2011 this volume hence understanding the diffusion of volatiles in melts provides a necessary tool for modeling bubble nucleation and growth however the diffusivities of volatiles such as h2o co2 so2 and h2s in the melt do not only affect the degassing rate they may also cause a fractionation of volatiles between gas phase and melt as well due to different diffusivities for instance in hydrous magmas the diffusion of h2o is usually much faster than co2 and sulfur diffusion baker et al 2005 zhang and ni 2010 so rapid disequilibrium removal of bubbles from the melt may cause an artificial enrichment of some components in the bubbles other processes which may be governed by sulfur diffusion in the melts are the dissolution and precipitation of minerals in glass manufacturing crucial problems are the kinetics of dissolution of the raw materials in the melt batch and of

geochemical characteristics of the miocene eolian deposits in china their provenance and climate implications 1 in the loess plateau in northern china the quaternary loess soil sequences the hipparion red earth of eolian origin red clay and the miocene loess soil sequences constitute a near continuous terrestrial record of paleoclimates for the past 22 ma in this study miocene loess and paleosol samples from qinan qa i were analyzed for their major trace and rare earth element chemistry and compared with the pliopleistocene samples from xifeng with emphasis on their provenance and paleoclimatic implications the results show similar geochemical signatures for the eolian deposits of different ages and they are also comparable to the average composition of the upper continental crust these suggest that the dust materials were all derived from well mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes they also support the notion of broadly similar source areas and dust transporting trajectories for different periods since the early neogene the slightly higher k2o fe2o3 and mgo concentrations and loss on ignition values and the lower na2o content in the miocene loess samples compared to their quaternary counterparts are attributable to the finer grain size of the miocene loess associated with weaker dust carrying winds in comparison with some loess in europe and america with less extensive sources eolian deposits from northern china show higher cs and lower zr and hf content this is attributable to the sorting processes from remoter sources during transportation and could be regarded as an indication of the desert origin of the loess deposits miocene paleosol samples show higher chemical index of alteration values and lower cao mgo and na2o concentrations than does the intervening loess indicating stronger weathering of the paleosols however the moderate chemical weathering of the paleosol samples indicates a constant semiarid and subhumid climatic range in northern china since the early miocene components 9791 words 8 figures 3 tables

stabilities of laurite rus2 and monosulfide liquid solution at magmatic temperature we have reversed the equilibria ru s2 rus2 and 2feo s2 2fes o2 under controlled temperature oxygen fugacity fo2 and sulfur fugacity fs2 at 1 atm to test if the platinum group mineral laurite rus2 has a stability field at magmatic temperature outside that of magmatic monosulfide liquid the fs2 in equilibrium with ru and rus2 is given by log fs2 6 9 12190 t 1173 to 1673 k whereas the fs2 at sulfide saturation of a basaltic melt may be approximated from log fs2 6 7 12800 t 2 log xfeo log fo2 1473 to 1673 k our experiments support the notion that the sulfide mineral laurite can crystallize directly out of a sulfur bearing sulfide undersaturated silicate melt as implied by laurite chromite intergrowth textures in natural chromite ore

os isotopes as tracers in seafloor hydrothermal systems metalliferous deposits from the tag hydrothermal area 26 n mid atlantic ridge abstract os isotopic analyses of a suite of samples from the tag hydrothermal area 26 n on the mid atlantic ridge reveal evidence of release of ocean crust derived os to seawater and removal of seawater derived os to the seafloor 187 os 186 os ratios of sulfide samples from the active tag mound vary between 8 7 and 1 3 the highest ratios are indistinguishable from the inferred 187 os 186 os ratio of seawater the incorporation of seawater derived os in these samples is interpreted as evidence of both entrainment of seawater into hydrothermal fluids and the addition of seawater os to samples during sulfide oxidation several sulfide samples from the active tag mound have 187 os 186 os ratios lower than the inferred seawater value with the lowest ratio approaching values expected for pristine oceanic crust these low 187 os 186 os ratios indicate that os derived from alteration of the oceanic crust is released to seawater in association with venting of high temperature hydrothermal fluids precipitates from low temperature hydrothermal fluids fe and mn oxide deposits from the east wall of the axial rift valley also have low 187 os 186 os ratios 4 2 6 8 relative to seawater these data suggest os isotopes may be sensitive tracers of low temperature hydrothermal circulation on the seafloor and that supply of ocean crust derived os to seawater is not strictly limited to high temperature hydrothermal vents the os concentration and isotopic composition of metalliferous sediment samples from a push core collected 125 m from the base of the active tag mound are also reported in this core metalliferous sediment horizons derived from mass wasting of altered sulfides exhibit variable 187 os 186 os ratios 4 8 8 7 reflecting mixing of seawater derived and ocean crust derived os in contrast sediments in which the metalliferous component is derived from fall out of hydrothermal material from the neutrally buoyant hydrothermal plume have 187 os 186 os ratios which vary over a narrow range 8 6 8 7 and appear to accurately record the os isotopic composition of seawater

diagenesis of magnetic minerals in the recent sediments of a eutrophic lake magnetic mineral assemblages in lake sediments are usulally interpreted as reflecting changing catchment erosion magnetic and chemical assemblages in a small eutrophic lake lough augher northern ireland suggest diagenetic dissolution of fine grained magnetite however probably as a result of changing redox conditions associated with eutrophication water column results show internal cycling of mn and fe from the sediments into the armxic hypolimnion calculations suggest that late summer hypolimnetic fe concentrations are controlled by formation of aulhigenic vivianite sedimentary pore water concentrations of total soluble fe and p suggest a similar process in the sediments the loss of mn from the lake by diffusion from the sediment and washout at overturn is indicated by mn budget calculations and by it marked decrease in its sedimentary concentration reflecting onset of eutrophication as indicated by diatom biostratigraph y the changes in the sediment mn profile are coincident with and in some cases identical to changes in several rnagnctic parameters the changes in magnetic stratigraphy suggest a coarsening of the magnetic grain size and reduction in the total concentration agreement with chemical profiles indicative of changing rcdox suggest that this coarsening results from dissolution of fine grained magnetite catchment stability together with other stratigraphic profiles of eutrophication and changing redox supports the conclusion that the magnetic profiles are reflecting in situ diagenetic changes rather than altered catchment processes with the data available it is not possible to identify the actual clissolution process involved or to determine whether it is chemically or bacterially controlled

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

the magnetic properties of particle sized samples from the luo chuan loess section evidence for pedogenesis abstract measurements of magnetic susceptibility and of laboratory remanences have been carried out on particle size fractions of loess and palaeosol samples from luo chuan china they show that the sub micron clay fraction of the palaeosol is greatly enriched in fine grained

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

s cl f degassing pattern of water rich alkali basalt modelling and relationship with eruption styles on mount etna volcano abstract our knowledge of the degassing pattern of sulphur chlorine and fluorine during ascent and eruption of basaltic magmas is still fragmental and mainly limited to water poor basalts here we model and discuss the pressure related degassing behaviour of s cl and f during ascent differentiation and extrusion of h2o co2 rich alkali basalt on mount etna sicily as a function of eruptive styles our modelling is based on published and new melt inclusion data for dissolved volatiles co2 h2o s cl f in quenched explosive products from both central conduit 1989 2001 and lateral dyke 2001 and 2002 eruptions pressures are obtained from the dissolved h2o and co2 concentrations and vapour melt partition coefficients of s cl and f are derived from best fitting of melt inclusion data for each step of magma evolution this allows us to compute the compositional evolution of the gas phase during either open or closed system degassing and to compare it with the measured composition of emitted gases we find that sulphur chlorine and fluorine begin to exsolve at respective pressures of 140 mpa 100 mpa and 10 mpa during etna basalt ascent and are respectively degassed at 95 22 55 and 15 upon eruption pure open system degassing fails to explain gas compositions measured during either lateral dyke or central conduit eruptions instead closed system ascent and eruption of the volatile rich basaltic melt well accounts for the time averaged gas composition measured during 2002 type lateral dyke eruptions s cl molar ratio of 5 1 35 bulk cl loss extensive magma fragmentation during the most energetic fountaining phases enhances cl release 55 and produces a lower s cl ratio of 3 7 as actually measured comparatively slower magma rise in the central conduits of etna favours both sulphide saturation of the melt and greater chlorine release 55 resulting in a distinct s cl evolution path and final ratio in eruptive gas in both eruption types any previous bubble melt separation at depth leads to increased s cl and s f ratios in emitted gas high s cl ratios measured during some discrete eruptive events can thus be explained by transitions from closed deep to open shallow system degassing with differential gas transfer extending down to 2 km depth below the vents this depth coincides with the base of the volcanic pile where structural discontinuities and the high magma vesicularity 60 may favour separate gas flow finally the excess s cl f gas discharge through etna summit craters during non eruptive periods requires a mixed supply from shallow magma degassing in the volcanic conduits and deeper derived so2 rich bubbles from the sub volcano plumbing system our modelling provides a useful reference framework for interpreting the monitored variations of s cl and f in mount etna gas emissions as a function of volcanic activity more broadly the observations made for s cl and f degassing on etna may apply to other basaltic volcanoes with water rich magmas such as in arcs

anhydrite stability and the effect of ca on the behavior of sulfur in felsic magmas the distribution of sulfur in the system na2o k2o cao al2o3 sio2 h2o s was investigated at 2 kbar 750 950 c and oxygen fugacities ranging from the co coo to the re reo2 buffer anhydrite caso4 crystallized in all the experiments conducted at oxidizing conditions ni nio 0 5 to 1 and above under otherwise equal conditions an inverse relationship between sulfur and cao concentration was observed in melts coexisting with anhydrite with the solubility product k cao so3 being constant where cao and so3 are the molar fraction of cao and so3 in the quenched glasses this suggests that anhydrite dissociates upon dissolution in the melt according to caso4 anhydrite ca2 melt so42 melt the solubility product strongly depends on temperature with lnk 28 573 917 t 11 26 0 80 this corresponds to an enthalpy of dissolution of h r 237 5 7 6 kj mol under reducing conditions co coo and ni nio buffer cao has no effect on the fluid melt partition coefficient of sulfur d sfluid melt at 850 c 2 kbar partition coefficients were 519 30 at the ni nio buffer and 516 11 at the co coo buffer for cao contents in the melt up to 1 wt these data are virtually identical to those measured in the cao free haplogranite system under reducing conditions however under more oxidizing conditions the fluid melt partition coefficient of sulfur appeared to have increased somewhat in the presence of cao this increase may however also be related to the fact that the final melt compositions in these runs were distinctly peraluminous our data show that calcium has no effect on the degassing of sulfur at reducing conditions but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

hematite formation by oxygenated groundwater more than 2 76 billion years ago geoscientific drilling in the marble bar area of the pilbara craton western australia resulted in the discovery of locally abundant hematite in archean basalts 200 m below the present land surface the hematized basalts occurring along a bedding parallel shear zone are cross cut by pyrite veinlets 3 mm in width and contain euhedral pyrite grains 10 500 m in diameter with sharp crystal edges indicating that the hematite formed before the pyrite we have dated the pyrite in the veinlets at 2 763 0 016 ga using the re os method therefore the hematite formed prior to 2 763 ga the basalts containing the hematite belong to the apex basalt of the warrawoona group and were erupted onto the archean seafloor at 3 46 ga due to 2 9 ga orogenic deformation and subsequent deep erosion the apex basalt was exposed at the surface of a continental landmass prior to 2 77 ga sometime in the period between 2 9 ga and 2 77 ga the basalt section we describe was less than 200 m below the late archean land surface and within range of groundwater percolation through the shear zone in the basalts geological mineralogical and geochemical lines of evidence strongly suggest that the infiltration of o2 rich groundwater through the bedding parallel shear in the basalts formed hematite prior to 2 76 ga and hence oxygenated surface environments at least localized and or short lived emerged more than 300 million years before the widely accepted great oxidation event during 2 45 and 2 32 ga