formation of native iron in sediment contaminated magma i a case study of the hanekammen complex on disko island west greenland abstract for the first time a compositional range of native iron bodies is described in a cogenetic series of sediment contaminated volcanic rocks from the tertiary west greenland basalt province the iron bearing rocks occur in a high level composite intrusion the hanekammen complex reaction between a tholeiitic parent magma with 11 mgo and carbonaceous al2o3 rich shale took place in a reservoir 3 km below the paleosurface and created magmatic layering with basaltic magma overlain by less dense andesitic magma the contaminated rock series bears a strong imprint of assimilation but very little fractional crystallization which implies that the two processes were not intimately coupled in the present case most of the iron was formed at depth in a range of fo2 from 10 13 atm 1200 c to 10 16 atm 1100 c as determined by the p distribution between solid iron and magma this is far below the graphite gas cco buffer at the estimated pressure 800 bars and suggests a high hydrogen fugacity together iron in basalt and andesite form a general trend defined by co versus ni concentrations that reflects the degree of assimilation the amount of immiscible sulphide liquid and the degree of reduction in order of decreasing importance the zoning of single iron grains reflects the dynamics of their growth and to some extent subsequent homogenization and reaction with the magma weakly zoned iron spherules in viscous andesite were formed and remained in situ whereas iron grains in basalt settled through the layered magma and developed strong zoning all iron types contain co rich domains

phosphoran olivine overgrowths implications for multiple impacts to the main group pallasite parent body phosphoran olivine 1 7 wt p2o5 is a metastable phase known from fewer than a dozen meteoritic or terrestrial occurrences we have thoroughly examined phosphoran olivine in the springwater pallasite to characterize its distribution textural relationships and geochemistry phosphoran olivine is abundant in springwater as randomly distributed millimeter scale partial overgrowths on the p free olivine crystals geochemical analyses support the substitution mechanism of p into the tetrahedral si site with octahedral site vacancies for charge balance observed trace element variations on the other hand are not related to p substitution element mapping reveals fine scale oscillatory p zoning in unusual serrate patterns indicating rapid crystal nucleation from a melt as proposed by boesenberg and hewins 2010 and a subsequently variable rate of crystallization the timing of phosphoran olivine formation in springwater is constrained to after the period of macroscopic olivine rounding but before the cooling of the metal matrix because the phosphoran overgrowths overprint specific host grain boundary modifications we suggest that the episode of extremely rapid cooling necessary to crystallize and preserve this rare phase may have been triggered by an additional impact to the parent body

formation of iron carbon alloys in basaltic magma at uivfaq disko island the role of carbon in mafic magmas two types of metallic iron were identified in a collection of samples from the tertiary iron bearing basalts of uivfaq disko island greenland high carbon iron has 2 9 4 0 wt carbon and eutectic textures of iron and cohenite fe 3 c similar to those of commercial white cast iron it occurs in approximately spherical bodies up to 15 mm in diameter that appear to have been immiscible metallic liquids within basaltic magma low carbon samples have 1 8 2 0 wt carbon and textures similar to those of commercial hypereutectoid steel they occur principally as large up to 22 tons cumulate masses both types of metal could have crystallized at low pressure from iron carbon liquids of their present bulk carbon contents fe ni co cu and p oxides in basaltic magma were reduced by carbon derived principally from assimilated cretaceous tertiary sediments niand ni cu ratios of the metal are similar to those of terrestrial basalts the magma contained excess carbon graphite so the metal formed as

aeolian abrasion and modes of fine particle production from natural red dune sands an experimental study a series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles 125 m by 1 the release of resident fines 2 spalling chipping and breakage of particles and 3 the removal of grain surface coatings parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass test tube chamber for up to 120h the fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle size analyses using a coulter multisizer the abrasion of untreated parent samples produced fine particles in one of two main size classes 50 m but when the parent sample was sieved to exclude particles 250 m relatively more material in the range 10 50 m was produced for unsieved parent samples the size range associated with the dominant mode varied according to the length of the abrasion time the coarsest mode 63 m was dominant during the first 16 h of abrasion then became less significant and is thought to be associated with the release of resident fines into suspension the finest mode 10 m was absent or very weak during the first 16h of abrasion then became more significant and in some instances dominated the distribution as abrasion continued removal of grain surface coatings is the main source of fine material 10 m and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles by comparison with previous studies of aeolian particle abrasion these natural dune sands produced very low quantities of fine material by weight but their spatial extent makes them potentially a significant source of dust sized particles at the global scale

rivers and loess the significance of long river transportation in the complex event sequence approach to loess deposit formation abstract rivers are essential for loess deposit formation river systems which relate directly to loess deposit formation include the danube and the rhine the mississippi and the missouri the thames and the medway the indus ganges and brahmaputra the dnepr don and volga the clutha mataura and rakaia new zealand rivers the yellow river rivers in south america siberian rivers flowing north the odra and the wisla between the mountains and the ice the syr darya and amu darya into the desert the contention is that rivers are not just important in major loess deposit formation they are mandatory necessary imperative obligatory essential indispensable requisite for a complete and satisfactory study of a loess deposit we need to know how the material is produced how it is transported and distributed across the landscape how intermediate deposits are formed how transportation provides the defining properties i e open structure collapsibility draping across the landscape and what may happen post deposition e g chernozemisation fragipan formation increased collapsibility etc if rivers are essential then it would appear that the british loess is probably alpine material delivered by the proto rhine and the polish loess is not derived from the ice sheet to the north but from the mountains to the south the lack of loess in canada is explained by the absence of suitable rivers the loess in russia and neighbouring countries can be classified as jefferson et al jefferson i f evstatiev d karastenev d mavlyanova n g smalley i j 2003b the engineering geology of loess and loess like deposits a commentary on the russian literature engineering geology 68 333 351 suggested on the basis of associated rivers a new deposit of glacial loess is recognised associated with the dnepr don and volga rivers the uswr loess the smalley leach smalley i j leach j a 1978 the origin and distribution of the loess in the danube basin and associated regions of east central europe a review sedimentary geology 21 1 26 available from www geo edu ro sgr mod downloads pdf smalley sedgeo 1978 pdf vision of the loess in the danube basin and east central europe is probably misconceived they assigned a great significance to glacial action and put loess in a northern band it appears that this proposed glacial influence is minimal and that the danube loess is essentially mountain loess derived from the alps the carpathians the sudeten mountains and other high regions the danube system is a classic example of a river controlling loess distribution

making loess sized quartz silt data from laboratory simulations and implications for sediment transport pathways and the formation of desert loess deposits associated with the sahara abstract results from a series of laboratory simulations designed to investigate quartz silt generation by a number of geomorphic mechanisms are reviewed these findings are then used to discuss potential sediment pathways involved in the formation of desert loess deposits and a pathway is presented to show a proposed sequence of events involved in the formation of the loess deposits associated with the sahara the results indicate that both fluvial and aeolian systems can be very effective at producing quartz silt it is suggested that fluvial systems within hot desert environments may play a central role in both the production and distribution of loessic silt first the highly energetic but periodic fluvial regimes associated with arid and semi arid environments may be responsible for considerable quantities of particle comminution second the intermittent nature of these systems will help maintain geomorphologically active surfaces from which silt sized material can be easily deflated as well as fluvial comminution a range of weathering mechanisms and aeolian abrasion may also be responsible for the generation of silts in desert loess consequently silt sources and mechanisms of silt generation are likely to be much more diverse for desert loess than those associated with glacial loess

multiple dust sources in the sahara desert the importance of sand dunes 1 we determine the current sources of dust in the sahara desert using quantitative correlation between the number of days with dust storms nds derived from remote sensing data of high temporal resolution with the distribution of the soil types and geomorphic units during 2006 8 the source of over 90 of the nds was found to be sand dunes leptosols calcisols arenosols and rock debris in contrast to previous studies only few dust storms originated from playas and dry lake beds land erodibility was estimated by regressing the nds to the number of days with high speed wind events and was found to be high for sand dunes clay and fine silt grains and aggregates are scarce in sand dunes which most likely produce dust particles through aeolian abrasion of sand grains thus saltating sand grains impacting clay aggregates on playa surfaces cannot be the sole process for generating dust in the sahara

silt production as a function of climate and lithology under simulated comminution production of the silt sized particles composing loess represents a critical step in its ultimate formation but the volume and rate of production in different settings remain underdetermined this study addresses the influence of climate and source lithology on silt formation by subjecting natural alluvial fluvial sand from systems characterized by varying climatic setting to simulated comminution bulk samples from comparable transport distances were collected from a hot arid california desert alluvial system hot humid puerto rico fluvial system and cold humid norway proglacial fluvial system and sieved to isolate the coarse very coarse sand fraction for experimental milling source rocks in all three systems consist of granitoids with some contributions from foliated coarse grained metamorphic rocks gneissic and schistose in norway results indicate that contributions from coarse grained foliated lithologies impart a negligible effect on rate of silt production from the sand starting material climatic setting imparts no significant difference on sand durability but influences clay production at later stages of comminution for the puerto rico sample presumably owing to the effects of deep chemical weathering prior to physical transport comminution and silt production in all experiments exhibit exponential decay wherein rapid initial rates diminish with time this is interpreted to reflect the effects of the dynamic milling conditions particle size and distribution and slurry viscosity as well as particle strength with the latter including both relative strengths of different minerals in general and the influences of lattice defects and microfractures in quartz in particular empirical observations reveal that silt fractions of the natural alluvial fluvial samples collected at comparable transport distances 5 7 km in the respective systems exhibit significant differences bulk sediment samples from the norwegian proglacial system contain substantially more silt 3 10 times than either of the other two localities implying a significant difference in the natural processes operating to generate silt in these different field settings we suggest this difference reflects the efficacy of glacial grinding in silt production

making the material the formation of silt sized primary mineral particles for loess deposits abstract in 1911 e e free wrote it may be well to point out that there are really two problems of the loess a problem of the origin of material and a problem of deposition the problem of the origin of material has been relatively neglected in comparison to problems of deposition of the formation of deposits and latterly in comparison to studies of loess stratigraphy if we are to understand the true nature of loess this fascinating material we need to be aware of all the significant events in the processing of the particles which form a deposit a large amount of silt sized primary mineral material has to be produced to make a loess deposit loess is a quaternary phenomenon and we see the entire process being completed in quaternary times some powerful quaternary forces are able to produce very large amounts of granular material glacial grinding vigorously supported by smalley 1966a provides an obvious source for some loess material but the vast deposits of north china and central asia have no obvious glacial connection however they are adjacent to high asia a region of vast tectonic activity and an enormous release of terrestrial energy in the last several million years high asia is a large producer of loess silt much of which finds its way south to make the ganges delta but large amounts are moved north and east to make huge loess deposits africa presents a problem recent work e g coude gaussen 1987 suggests that there is a region of peri saharan loess but earlier observations e g penck indicate quite clearly that the sahara region is free of loess rathjens 1928 in his study of tripolitania indicated the presence of loess like deposits and described their nature but he did point out that 90 of the granular material was greater than 100 pm in diameter which would remove it from a strict loess definition on the soil taxonomy map of africa there is a belt of soil d3 which could include considerable loess deposits it stretches from the matmata loess in tunisia across northern libya to the western part of the egyptian coastal region if d3 contains loess this points to a genuine desert loess particle producing mechanism operating in the sahara

an experimental investigation into the metastable formation of phosphoran olivine and pyroxene abstract the formation of phosphoran olivine by crystallization from a melt was investigated experimentally using a one atmosphere furnace using san carlos olivine mg fe 2 sio 4 mixed with either iron phosphide fep or magnesium pyrophosphate mg 2 p 2 o 7 both dynamic crystallization and isothermal experiments produced phosphoran olivine as zoned single crystals and as overgrowths surrounding normal phosphorus free olivine grains the crystallization pathways that form phosphoran olivine were traced and confirm that it is a metastable phase that can crystallize from a phosphorus rich melt over timescales of hours to days removal of the p and equilibration of the olivine however requires weeks to months in the presence of silicate melt phosphoran olivine with up to 27 wt p 2 o 5 was generated and up to 69 of the si tetrahedral sites were replaced by p the substitution of si by p into olivine was confirmed as 4 vi m 2 2 iv si 4 3 vi m 2 2 iv p 5 vi phosphoran olivine compositions that vary from mg fe 2 sio 4 to mg fe 1 65 0 35 si 0 3 p 0 7 o 4 have been produced in these experiments phosphoran pyroxene was also generated in a few experiments and forms when phosphoran olivine reacts with either tridymite or melt it has compositions compatible with protopyroxene orthopyroxene pigeonite and sub calcic augite and can contain up to 31 5 wt p 2 o 5 like phosphoran olivine it is also a metastable phase phosphorus replaces si in pyroxene by the following substitution methods 8 iv si 4 3 iv si 4 4 iv p 5 iv with al entering the structure by the exchange 2 iv si 4 iv al 3 iv p 5 phosphoran pyroxene compositions vary from mg fe 8 si 8 o 24 to mg fe 8 si 3 p 4 o 24

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

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

formation of phosphorus rich olivine in dar al gani 978 carbonaceous chondrite through fluid assisted metamorphism phosphorus rich olivine p 2 o 5 1 wt is a mineral that has been reported only in a few terrestrial and extraterrestrial occurrences previous investigations suggest that p rich olivine mainly forms through rapid crystallization from high temperature p rich melts here we report a new occurrence of p rich olivine in an ungrouped carbonaceous chondrite dar al gani dag 978 the p rich olivine in dag 978 occurs as lath shaped grains surrounding low ca pyroxene and olivine grains the lath shaped olivine shows a large variation in p 2 o 5 0 5 5 wt the p rich olivine grains occur in a chondrule fragment and is closely associated with chlorapatite merrillite feni metal and troilite tiny cr rich hercynite is present as inclusions within the p rich olivine the lath shaped texture and the association with cr rich hercynite indicates that the p rich olivine in dag 978 formed by replacing low ca pyroxene precursor by a p rich fluid during a thermal event rather than by crystallization from a high temperature melt the large variation of p 2 o 5 within olivine grains on micrometer scale indicates a disequilibrium formation process of the p rich olivine the occurrence of p rich olivine in dag 978 reveals a new formation mechanism of p rich olivine

possible formation mechanisms for the modal coarse silt quartz particles in loess deposits abstract the first major event in the formation of a loess deposit is the production of silt sized quartz particles many particle production methods have been proposed the bulk of loess particles appear to be produced by a glacial grinding to give ice sheet loess or b cold weathering in high regions to give mountain loess there are close relationships between mountain loess and desert loess loess material can be seen as a product of the cold phase of the glacial cycle

ellenbergerite a new high pressure mg al ti zr silicate with a novel structure based on face sharing octahedra ellenbergerite occurs as purple millimetre size grains associated with talc kyanite clinochlore rutile and zircon in composite inclusions within decimetre large pyrope crystals 90 98 mole percent end member in the quartzite layer of the dora maira massif western alps from which coesite has been recently reported chopin 1984 it is hexagonal a 12 255 8 c 4 932 4 a z 1 space group p63 mohs hardness 6 5 dmes 3 15 dcal 3 10 no cleavage uniaxial negative and vividly pleochroic colourless e colourless to deep lilac with colour zoning the intensely coloured variety has 1 6789 5 e 1 670 1 microprobe analysis yields sio2 39 1 p2o5 0 45 al2o3 25 1 tio2 4 0 mgo 22 2 feo 0 20 sum 99 05 wt including h2o 8 0 coulometrically the formula calculated on a o28 oh 10 basis implying 7 5 wt h2o is mg6 71 fe0 03 ti0 61 al6 00 si7 92 p0 08 o28 oh 10 the colour zoning is due to nearly complete ti zr substitution in addition ellenbergerite may contain more than 8 wt p2o5 with strictly correlated changes of si mg al and ti zr contents over 80 of which represent the sial pmg substitution

petrogenesis of uivfaq iron disko island greenland massive blocks of native iron and iron carbide weighing up to 22 tons have been found at uivfaq disko island western greenland the iron blocks are associated with tertiary basalts that erupted during rifting between greenland and baffin island early in the opening of the davis strait the iron is an asemblage of iron and iron carbide cohenite and various silicate sulphide and oxide inclusions containing highly reduced and iron rich phases including fayalite wustite troilite ulvospinel ilmenite ferriferous pigeonite and feo rich glass the chemistry and petrography of the inclusions are used to derive a paragenetic history for the uivfaq iron assemblage petrographic study of a massive uivfaq iron block shows that the block formed through accumulation of partly molten spherules of iron and cohenite 0 5 to 1 0 mm in diameter basaltic liquid was trapped by the accumulating metal spherules and reacted with the metal to form various highly reduced and iron enriched immiscible liquids these liquids solidified as inclusions in the iron mass various models are considered for the origin of the iron cohenite spherules at present a carbon reduction mechanism is preferred the association of graphite rich plagioclase spinel xenoliths thought to be derived from sediments with the iron masses suggests a genetic relation between the two we suggest that graphite was assimilated by mantle derived basaltic magma the carbon reduced iron oxide components of the basalt at a depth of 3 km or less and formed small immiscible droplets of high carbon iron carbon liquid these droplets were erupted with the magma the droplets settled and accumulated near or at the base of a flow or sill to form massive iron blocks

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

seventh foray whitlockite rich lithologies a diopside bearing troctolitic anorthosite ferroan anorthosites and kreep seventeen nonmare samples most of them pristine are characterized and implications of the new data are discussed five pristine samples are from apollo 14 near the center of the kreep rich zone in the moon s western hemisphere three of them are alkali anorthosites rich in ca phosphate whitlockite which apparently crystallized from magmas with ree contents roughly 6 those of high k kreep the alkali anorthosites probably formed from mg rich magmas that assimilated large amounts of urkreep but some might have formed by metasomatism of ferroan anorthosite by urkreep the gabbronorite norite classification scheme is not well suited to western hemisphere lithologies probably due mainly to the overriding effects of longitude petrochemistry correlations a diopside bearing mg rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic high ca pyroxene rich mg rich magmas and suggests that some source regions of mg rich magmas were relatively ca rich several pristine kreep fragments from apollo 15 station 2 are texturally and compositionally much like other pristine kreep and thus reinforce the evidence that kreep is highly uniform the pristine anorthosites on the other hand demonstrate further that lunar anorthosites are diverse

static breakage of granitic detritus by ice and water in comparison with breakage by flowing water temperature cycling between 4 5 1 0 c and 13 0 2 0 c in the presence of added water caused significant breakage of granitic detritus because cycling with only adsorbed water present also caused breakage fragmentation is attributed to both the combined action of ice and adsorbed water and to the latter acting alone breakage evidently resulted from the gradual tensile opening of pre existing cracks weakening then splitting grains surviving unbroken grains show evidence of a fatigue effect quartz split dominantly along pre existing subplanar microfractures whereas feldspar and biotite split along crystal cleavages degree of breakage and product size distribution depend on the crystalline nature of the parent material its previous history and the nature and duration of the breakage process with the first two factors the same size distributions from adsorbed water breakage alone and from that due to adsorbed water plus ice differ slightly both contrast strongly with those of simulated fluviatile breakage whereas the latter preferentially produced 2 20 m particles probably debris of inter particle collisions static breakage split coarser grains wherever major weaknesses occurred producing less selective product size distributions with greater proportions of loess sized material about 20 60 characteristic inflections in the size distribution curves of our experimentally produced debris are also shown by samples from the sola of some frost affected soils partially healed microfractures in plutonic quartz are normally spaced at about 1 10 approaching the downward asymptotic comminution limit for brittle solids about 1 surficial physical processes are capable of reducing only a small proportion of plutonic quartz to this size before its storage in sediments

origin of desert loess from some experimental observations a longstanding problem of quaternary geology has been the origin of the silty deposit known as loess of the many explanations for its formation and distribution1 2 the most commonly accepted is that the silt is produced by subglacial grinding processes1 3 4 followed by redistribution and deposition by the wind the large expanses of loess in central europe are therefore considered to be the consequence of quaternary glaciation5 there is however a view6 7 that loessic silt may also originate as the product of processes in hot deserts some proponents of the desert loess hypothesis consider that silt size material is the product of weathering processes7 which may include salt weathering8 or weathering down incipient cracks9 an alternative mechanism is aeolian attrition of sand grains although probably as a result of the experimental work of kuenen10 smalley and krinsley11 consider that only fine silt 2 6 m is produced in large quantities by the abrasion of quartz grains we have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts the products of abrasion show that both coarse and fine silt sizes are produced these findings suggest that desert aeolian processes can produce loess we also suggest that much of this material from many deserts has been deposited in the sea but that the chinese loess could have been produced in the gobi desert the finest particles produced by such attrition may be a source of silica for silcrete formation

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

the northwest africa 8159 nwa 8159 martian meteorite part 2 spinel orthopyroxene intergrowths a record of fo2 and crust basalt interactions abstract in part 1 of our examination of martian meteorite northwest africa 8159 nwa 8159 we illustrated many interesting mineralogical and textural attributes that make this martian basalt unique unlike the shergottites that illustrate a clear relationship between the extent of trace element and isotopic characteristics and oxygen fugacity reduced depleted magmas oxidized enriched magmas nwa 8159 illustrates a decoupling of this relationship as it has oxidized and depleted signatures in part 2 using a series of new observations and measurements cl isotopes xanes tem empirical modeling we use nwa 8159 to explore the interaction between mantle derived magmas and the martian crust the magnetite orthopyroxene intergrowths associated with olivine are a product of a martian subsolidus oxidation event near the qfm buffer and not a magmatic reaction in an oxidizing magma qfm 3 this subsolidus event is further supported by cr valence in the olivine alteration of p rich olivine and end member magnetite in the matrix of the meteorite although this subsolidus alteration makes it extremely difficult to determine the original fo2 of the parental magma for nwa 8159 there is evidence that during the initial stages of crystallization the fo2 was modestly reducing iw 1 potential manifestations of more reducing magmatic conditions include p rich cores in the olivine and low fe3 in silicates plagioclase pyroxene further if analogous to all other depleted shergottites nwa 8159 initially crystallized under reducing conditions this decoupling between oxygen fugacity and isotopic trace element characteristics suggests that basalts derived from the martian mantle interacted with the crust in ways that significantly influenced redox history and volatile element isotopic composition cl s without dramatically modifying many of its radiogenic isotope and trace element mantle fingerprints

an overview of the role of weathering in the production of quartz silt abstract quartz silt is a widespread detrital sediment with large aeolian loess and alluvial silt deposits forming important components of many contemporary landscapes despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments e g glacial grinding fluvial comminution aeolian abrasion frost weathering salt weathering insolation weathering and deep weathering the glacial aeolian hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a quaternary phenomenon as a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre quaternary environments in particular earth scientists may have considerably underestimated the role of weathering in global silt generation as there are now many references to the existence of a patchy but widespread distribution of pre quaternary weathering profiles across the glacial and periglacial landscapes of the northern hemisphere e g north america british isles north and central europe landscapes within which many of the classical loess deposits are located these observations suggest that weathering profiles may have covered large tracts of the northern hemisphere land surface prior to the quaternary glaciations this in turn may have important implications for quartz silt generation as 1 experimental studies indicate that many weathering processes are capable of generating significant quantities of silt sized debris and 2 particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt sized material or quartz grains that are weakened by weathering derived microfractures thus weathering profiles may represent mines of actual and potential quartz silt available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial fluvial and aeolian erosion

trace elements in natural metallic iron from disko island greenland the largest occurrence of natural metallic iron on earth is on the island of disko greenland metallic iron is found there in a variety of different types from small metal particles in basalts to large meter sized blocks we have studied three different types of metallic iron small metal spherules 300 m in basaltic magma larger metal grains 300 m 3 mm often composed of aggregates of smaller particles in similar host rocks and massive iron lumps up to several tons analytical data for 13 siderophile elements in samples from these three types are presented all metals analysed have a distinctly crustal pattern of siderophile elements high co ni re ir or w ir ratios clearly demonstrate that a meteoritic origin for the metallic iron must be excluded since the co ni and re ir ratios are approximately chondritic in the upper mantle of the earth a mantle origin for the disko metals can also be ruled out this supports earlier petrological and geological evidence that the metallic iron was formed through reduction of basaltic magma by carbon derived from tertiary shales and coals significant differences in absolute and relative abundances of siderophile elements occur among the three kinds of metals the strongly siderophile elements e g ir re ni increase in concentration from the small metal spherules through the larger grains to the massive iron lumps the contents of less strongly siderophile elements p w ga decrease in the same sequence evidence is presented that the small metal spherules are formed by in situ reduction larger iron metal grains and massive iron lumps are composed of small spherules accumulated by gravitational settling in a magma reservoir these metal cumulates have extracted highly siderophile elements from a larger volume of basaltic melt

phosphoran pyroxene and olivine in silicate inclusions in natural iron carbon alloy disko island greenland a survey of literature data on the p contents of olivine pyroxene and garnet in mantle xenoliths and the bulk p contents of mantle xenoliths shows that available data is ambiguous as to whether mantle p is primarily contained in silicates or in phosphates even though phosphates are rarely observed in mantle xenoliths garnet probably contains more of the mantle s p than olivine or pyroxene bulk p contents of mantle xenoliths vary significantly estimation of the primitive mantle p content from xenoliths requires interpretation of the partial melting and contamination histories of the xenoliths

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

mechanisms of loess sized quartz silt production and their relative effectiveness laboratory simulations the production of loess sized quartz silt is frequently ascribed to glacial grinding mechanisms in this study a series of laboratory simulations was set up the purpose of which was to demonstrate that a range of geomorphic mechanisms are capable of producing silt under laboratory conditions the geomorphic mechanisms investigated were aeolian abrasion fluvial comminution glacial grinding salt weathering and frost weathering the results confirmed that under laboratory conditions all of these mechanisms were capable of producing silt the relative effectiveness of these mechanisms at producing silt under laboratory conditions was then calculated in order to provide a starting point for a consideration of their potential effectiveness within the natural environment these results indicate that fluvial and aeolian activity are highly effective at producing quartz silt over short time periods in a dust storm of four days duration 287 g of silt could potentially be produced from every kilogram of sand entrained while fluvial comminution in a turbulent fluvial environment could potentially produce 900 g of silt from every kilogram of sand entrained within 32 h over longer periods of time the glacial grinding and weathering mechanisms represent more continuous and hence more effective silt producing mechanisms although it is realised that the relative importance of each silt producing mechanism will differ spatially and temporally due to differences in climate relief geology and geomorphic history the findings from this work do have implications for the genesis of loess deposits they demonstrate that glacial and cold weathering processes are not solely responsible for fine particle formation and that efficient silt producing mechanisms can operate within a variety of environments under suitable conditions weathering together with episodic contributions from aeolian and fluvial mechanisms could be responsible for a considerable proportion of global quartz silt production

the formation of silt material for terrestrial sediments particularly loess and dust abstract there are certain controls which operate to demarcate the nature and size range of quartz particles in terrestrial detrital sediments the particles fall into discrete and definable populations which are separated by tanner gaps quartz sand nature is determined largely by a eutectic like reaction which takes place in the original igneous rock this reaction delivers a fine mix of quartz and feldspar units which on weathering deliver quartz sand the formation of quartz silt is more contentious it appears that silt production is essentially controlled by the presence in larger quartz particles of moss defects crystalline defects introduced into the quartz structure by earlier events e g the high low displacive transformation in cooling quartz there appear to be two modes in airborne quartz particles which have been called large dust and small dust the larger mode is the loess mode around 20 60 m and the smaller mode falls into the classification with high level long travel dust mode around 2 6 m the quartz in small dust is around the same size as the clay mineral agglomerate particles cma which form a considerable proportion of high level dust clouds the cma particles form from lake deposits the size is controlled by the openness of the packing in the lake sediments this can be demonstrated by a simple monte carlo model

experimental investigation of the partitioning of phosphorus between metal and silicate phases implications for the earth moon and eucrite parent body abstract the solid metal silicate melt partition coefficient for p d p has been determined experimentally at 1190 c and 1300 c the dependence of the partition coefficient on oxygen fugacity has been investigated and is consistent with a valence state of 5 for p in the silicate melt the experimental partition coefficients are given by log d p 1 21 log o 2 15 95 at 1190 c log d p 1 53 log o 2 17 73 at 1300 c the experimentally determined partition coefficients may be used to interpret the low p la ratios of the earth moon and eucrites relative to c1 chondrites the low p la ratios in the eucrites may be explained by partitioning of p into 5 to 25 of a sulfur bearing metallic liquid assuming equilibration and separation of the liquid metal from the silicates at low degrees of partial melting of the silicates the low w la ratios in the eucrites compared to c1 chondrites require the separation of an additional 2 to 10 solid metal the lowering of both p la and w la ratios in the moon may be explained by partitioning of p and w into metal during formation of a small core by separation of liquid metal from silicate at low degrees of partial melting of the silicates the w la ratios in the earth and moon are virtually indistinguishable while p la ratios differ by a factor of two the concentrations of feo also appear to be different these observations are difficult to reconcile with the hypothesis of a terrestrial origin of the moon following formation of the earth s core but are consistent with independent formation of the earth and moon

armalcolite bearing fe ti oxide assemblages in graphite equilibrated salic volcanic rocks with native iron from disko central west greenland native iron bearing strongly sediment contaminated andesitic to dacitic lavas from the malig t formation on disko contain an early phenocryst assemblage of plagioclase low ca pyroxene s and ilmenite the phenocrystic ilmenite has reacted to form complex fe ti oxide metal sulphide aggregates which contain one or more of the oxides ilmenite armalcolite and rutile the armalcolite is very similar to the lunar type 1 armalcolite of haggerty 1973 and approximate compositionally the ternary system feti2o5 mgti2o5 ti3o5 92 to 97 mol when evidence from several salic rocks is combined the fe ti oxide metal sulphide aggregates display reactions which may represent one isobaric invariant assemblage ilmenite armalcolite rutile iron and the 3 boundary univariant reactions in the system fe ti o the compositional and textural features of ferro magnesian silicates oxides and metals show that most rocks were affected by a rapidly declining fo2 during magma ascent and cooling as displayed in the fe ti oxide metal sulphide aggregates by the cross cutting of one or several t fo2 buffer curves in the system fe ti o prominent sulphidation reactions are observed in the oxide aggregates and are always of the type where feo in oxide is replaced by fes while the liberated oxygen is consumed in a reduction process carbon bound as graphite or cohenite occurs throughout the rocks and is mostly enclosed in phenocrysts and xenocrysts when the salic magmas ascended from pre eruption reservoirs at 1 to 1 5 kb the reduction was largely controlled by strongly pressure dependent carbon oxygen equilibria resulting in rapidly declining t fo2 paths recorded by the oxide assemblages in the simplified c o gas system carbon barometry sato 1979 applied to the selected rocks would indicate final equilibrium pressures of between 10 and 100 bars the scarcity of preserved graphite in the lavas would suggest that the carbon controlled reductions were terminated when available carbon was exhausted during the magma ascent and solidification

precious metal enrichment at low redox in terrestrial native fe bearing basalts investigated using laser ablation icp ms primary native fe is a rare crystallizing phase from terrestrial basaltic magmas requiring highly reducing conditions fo2 iron wustite buffer in order to form reducing conditions in basaltic magmas can be achieved through assimilation of carbonaceous crustal material which leads to formation of an immiscible molten c rich native fe alloy liquid if this liquid also contains sufficient sulfur it can undergo further division into conjugate fe c rich and a fe s rich immiscible melts that can effectively scavenge the highly siderophile elements hse re au and the platinum group elements pge pd pt rh ru ir os as well as ni and cu to economic abundances three localities are known globally where native fe bearing mafic rocks occur 1 paleocene basalts of disko island west greenland 2 a miocene lava of the buhl basalts germany and 3 mafic intrusions associated with the late permian siberian flood basalts in this contribution we report major and minor element compositions and hse concentrations for the main alloy phases feni metal and cohenite and sulfide for all three known global occurrences of native fe bearing basalt total hse abundances in metal grains obtained by laser ablation inductively coupled plasma mass spectrometry la icp ms are lowest in the buhl basalt 0 05 ppm intermediate in the disko island basalts 4 8 ppm and highest the siberian khungtukun and dzhaltul intrusions 10 30 ppm these differences demonstrate that while native fe formation is the result of carbonaceous crustal assimilation hse enrichment is not ubiquitous during this process the siberian occurrences are characterized by pt pge ppge pt pd enrichment relative to the ir pge ipge rh ru ir os consistent with models of early stage fractionation of olivine chromite and metallic ipge in staging magma reservoirs prior to the addition of c rich crustal materials in the shallow crust relative to noril sk ni cu pge sulfide ores the siberian native fe basalts are enriched in the ppge relative to the ipge but exhibit ru enrichments in contrast disko island native fe rocks do not show significant fractionation of the ppge from the ipge but have positive re and ru anomalies and high os ir ratios to reconcile these observations we present a general model where some parental melts experienced early stage crustal assimilation in staging magma reservoirs prior to reduction by carbon rich materials e g khungtukun dzhaltul whereas basaltic parental melts to disko island and buhl solely experienced interaction with carbonaceous material resulting in extensive devolatilization native fe segregation and native fe formation

alkremite garnetite and eclogite xenoliths from bellsbank and jagersfontein south africa alkremites garnet spinel orundum garnetites and eclogites garnet clinopyroxene from bellsbank and jagersfontein kimberlites show textural and mineralogical evidence of crystal fractionation from evolving aluminous magma e g ca and p increase in garnet as cr and ti decrease in most spinels detailed variations of cr and ti in garnet and spinel require several parental magmas corundum in alkremites contains 0 1 0 2 wt vo tioz 0 2 0 5 cr2o3 and 0 5 1 2 fezor mica 0 7 3 4 tioj in grain boundaries is secondary foundering or subduction of al rich sediments perhaps chloritized ocean crust may have generated local al enrichment in the upper mantle to provide diverse source regions for alkremite magmas

subglacial comminution in till evidence from microfabric studies and grain size distributions quartz feldspar and chlorite the principal minerals in a basal till from the halasi river catchment in the altay mountains northwestern china are present in approximately equal concentrations in the coarse fraction of the till 1 0 0 125 mm quartz concentrations are significantly higher than those of the other two minerals in the 0 125 0 016 mm size range feldspar and chlorite concentrations are higher than those of quartz in the finest fraction quartz has a strong preferred mode at 0 063 0 032 mm feldspar and chlorite have two weak modes in the silt size range one between 0 063 and 0 032 mm and the other between 0 016 and 0 004 mm thin sections of oriented impregnated samples were used to study crushing and abrasion over 2700 daughter particles were identified as products of comminution of 925 parent grains quartz and feldspar are most likely to be broken into two particles of roughly equal size as are fine chlorite grains however owing to their weakness and cleavage larger grains of chlorite tend to be split into more than two daughter particles sizes of the daughter grains were measured and sizes of the original parent grains were estimated mean parent grain sizes for quartz feldspar and chlorite are 0 129 0 078 and 0 059 mm respectively whereas mean daughter grain sizes are 0 068 0 041 and 0 024 mm respectively the greater percentage reduction in the size of chlorite reflects its tendency to break into more than two daughter particles most grains tend to be crushed only a few large particles seem to have suffered from abrasion

glacial comminution of quartz sand grains and the production of loessic silt a simulation study abstract traditional views have attributed the formation of loess sized quartz silt particles to glacial processes glacial grinding was considered to be the only mechanism capable of producing loessic silt in the quantities necessary for the formation of loess deposits this idea has been strengthened by the apparent close association between present or former glacierised regions and major global loess deposits however some doubts exist as to whether or not glacial grinding is capable of producing sufficient quantities of quartz silt because of the difficulties entailed in the observations and direct measurement of subglacial abrasion and crushing this paper describes and discusses the results of a simulation study designed to examine abrasion and size reduction of quartz grains under grinding conditions analogous to those experienced in a subglacial environment the findings from these experimental runs suggest that although particle breakage and comminution does occur little silt sized material is actually produced the amount of silt produced ranges from approximately 9 of the original sample in one experimental run to less than 1 for the other seven runs it is suggested that the results obtained may show considerably less abrasion and loessic silt production than may be expected to occur within a natural subglacial environment because 1 subglacial grains experience much greater overburden pressures for much longer periods of time 2 the use of sand sized grains may represent a stable component resistant to further size reduction through crushing or abrasion and 3 the use of a monomineralic sample of relatively sound quartz grains although care must be taken when relating results obtained from these experimental runs to silt production within a glacial environment findings from this work do question whether large amounts of quartz silts are produced within subglacial environments the importance of glacial processes in the formation of loess deposits may lie in the reworking of pre existing sediments by ice rather than the actual production of vast quantities of silt this in turn suggests that care should be taken in the interpretation of the provenance of particles comprising loess deposits

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds