geochemical and sr nd isotopic characteristics of cretaceous to paleocene granitoids and volcanic rocks se tibet petrogenesis and tectonic implications abstract northward subduction of the neo tethyan oceanic lithosphere beneath south asia gave rise to an andean type convergent margin with arc magmatism starting since at least the early jurassic and lasting until the eocene this study reports geochemical and sr nd isotope data of the early cretaceous 133 110 ma to paleocene 60 ma magmatic belt that formed in the eastern lhasa terrane se tibet including three major transhimalayan batholiths namely azhagong demulha and chayu and an early cretaceous volcanic succession from ranwu area all these rocks show relative enrichments in lile and lree and depletions in hfse corresponding to the geochemical characteristics of arc magmas from modern subduction zones while the azhagong batholith consists typically of metaluminous i type granitoids that occasionally contain mafic enclaves highly fractionated peraluminous s type and a type granites are observed from the chayu and demulha batholiths respectively these granitoids as a whole show heterogeneous sr and nd isotope ratios with e nd t varying from 1 5 to 13 and i sr from 0 703 to 0 745 the ranwu volcanic rocks which range from basaltic to dacitic compositions are calc alkaline in nature they have e nd t from 3 to 6 and i sr from 0 705 to 0 707 overlapping the isotopic range of the azhagong mafic enclaves the overall geochemical and sr nd isotope data suggest three magma source components involved in the petrogenesis which are the mantle wedge and the lower and upper parts of the lhasa continental crust accordingly we propose a two stage petrogenetic model involving 1 deep level differentiation of the mantle wedge derived mafic magmas associated with assimilation by the lower continental crust of the lhasa terrane and 2 additional differentiation and upper crustal contamination of the evolved magmas as they rise and install in shallow level magma chambers while the first stage can explain how the ranwu volcanics and azhagong enclaves formed the second accounts for the emplacement of the azhagong and chayu batholiths the shallow intrusions moreover may have caused low pressure melting of existing calc alkaline rocks of paleoproterozoic nd isotope model age to produce the early cretaceous 125 ma a type granites in the demulha batholith a specific rock type that occurs rarely in subduction zones but echoes with the notion for an extension setting in the region this setting may have taken place after the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes and interacted with the back arc evolution in the neo tethyan subduction system

rare earths behaviour during the deposition of volcanic sublimates abstract in this study the ree distribution between volcanic fluids and related solids in fumaroles with temperatures ranging from approximately 100 to 421 c was investigated in different geological scenarios the treatment of geochemical ree data was carried out by calculating the ree enrichment factors ef ree relative to the volcanic host rocks in studied sites under the assumption that the ree transport takes place as silicate aerosol in volcanic fluids shale normalised ree concentrations in these fluids have been assessed to investigate whether the ree transport as aqueous complexes in water saturated volcanic gas is reasonable the ree behaviour in alkaline condensates according to the above mentioned treatments of geochemical data is very similar being characterised by positive ce and gd anomalies and significant w type tetrad effects these evidences suggest that the geochemical behaviour of ree in fumarolic fluids is firstly influenced by the sublimate deposition along the fumarolic conduit or around the vents rather than by the transport mechanism of these elements in volcanic fluids the gd enrichment relative to its neighbours eu and tb induces the growth of positive gd anomalies recognised in condensates that in turn results in gd fluxes from the studied fumarolic systems ranging from 0 01 to 0 92 kg y 1 this indication represents a novelty in the well known geochemical gd behaviour where recognised positive gd anomalies have usually been attributed to anthropogenic contamination

glacier advance in southern middle latitudes during the antarctic cold reversal the geographic extent of cooling associated with the antarctic cold reversal is unclear dating of glacial moraines in new zealand suggests that the cooling extended into the southern mid latitudes possibly as a result of the northward migration of the southern subtropical front

influence of the tropics and southern westerlies on glacial interhemispheric asymmetry latitudinal variations in the location of the southern westerly wind belt have been associated with millennial scale climate variations during the last glacial period a reconstruction of sea surface temperatures off the southern coast of australia suggests that these climate variations also drove changes in the location of the oceanic subtropical front

experimentally determined si isotope fractionation between silicate and fe metal and implications for earth s core formation abstract stable isotope fractionation amongst phases comprising terrestrial planets and asteroids can be used to elucidate planet forming processes to date the composition of the earth s core remains largely unknown though cosmochemical and geophysical evidence indicates that elements lighter than iron and nickel must reside there silicon is often cited as a light element that could explain the seismic properties of the core the amount of silicon in the core if any can be deduced from the difference in 30 si 28 si between meteorites and terrestrial rocks if the si isotope fractionation between silicate and fe rich metal is known recent studies e g georg r b halliday a n schauble e a reynolds b c 2007 silicon in the earth s core nature 447 31 1102 1106 fitoussi c bourdon b kleine t oberli f reynolds b c 2009 si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core earth planet sci lett 287 77 85 showing sometimes subtle differences between 30 si 28 si in meteorites and terrestrial rocks suggest that si missing from terrestrial rocks might be in the core however any conclusion based on earth meteorite comparisons depends on the veracity of the 30 si 28 si fractionation factor between silicates and metals at appropriate conditions here we present the first direct experimental evidence that silicon isotopes are not distributed uniformly between iron metal and rock when equilibrated at high temperatures high precision measurements of the silicon isotope ratios in iron silicon alloy and silicate equilibrated at 1 gpa and 1800 c show that si in silicate has higher 30 si 28 si than si in metal by at least 2 0 these findings provide an experimental foundation for using isotope ratios of silicon as indicators of terrestrial planet formation processes they imply that if si isotope equilibrium existed during segregation of earth s core forming metal and silicate mantle there should be an isotopic signature of si in the core our experiments combined with previous measurements of si isotope ratios in meteorites and rocks representing the bulk silicate earth suggest that the formation of the earth s core imparted a high 30 si 28 si signature to the bulk silicate earth due to dissolution of 6 wt si into the early core

new ni and co metal silicate partitioning data and their relevance for an early terrestrial magma ocean abstract it is generally assumed that the abundances of the siderophile metal loving elements in the earth s mantle are the result of core formation in the early earth in the most popular model the low contents of siderophile elements in the earth s mantle are the result of metal silicate equilibration followed by metal accumulation at the base of a magma ocean this model is primarily based on the pressure dependence of ni and co metal silicate partition coefficients first determined by li and agee li j agee c b 1996 geochemistry of mantle core differentiation at high pressures nature 381 686 689 we have undertaken a further test of this hypothesis by performing a large number of additional partition experiments with the two key elements ni and co at a variety of temperatures and a pressure range extending from ambient pressure to 25 gpa 750 km depth in the earth the unexpected result of the new experiments is the recognition of two pressure regimes in the temperature and pressure dependences of ni fe and to a lesser extent of co fe exchange metal silicate partition coefficients k d ni fe and k d co fe the strong pressure and temperature dependences of k d ni fe and k d co fe at atmospheric pressure change below about 5 gpa to much weaker dependences at higher pressures as a consequence the pressure dependences of k d ni fe and k d co fe cannot be regressed with a single fit over the entire pressure range fits based on partition data obtained in this work and from the literature between 5 gpa and 25 gpa were extrapolated to pressures and temperatures to lower mantle liquidus conditions the co fe partition coefficients required to satisfy the present mantle composition is reached at about 35 gpa whereas the proper ni fe ratio requires 45 to 50 gpa at 55 gpa ni and co partition coefficients would be identical but the ni and co contents imposed on the earth s mantle by metal silicate equilibration would be too low this would exclude single stage magma ocean models for producing approximately chondritic ni co ratio in the earth s mantle however the accuracy of the experimental data obtained here and from the literature is not sufficient to unambiguously exclude single stage equilibration the results of this and other recent studies exclude that fe ni and co contents of the present upper mantle were established by metal silicate equilibration at upper mantle conditions

a model for granite evolution based on non equilibrium magma separation evidence from the gharib and qattar fluorite bearing granites eastern desert egypt we present 77 new granite whole rock analyses from the qattar and gharib areas eastern desert egypt both areas include a normal granite and either a hypersolvus gharib or an almost plagioclase free granite qattar enriched in fluorite according to earlier results f influences element distribution in granitic melts forming complexes with specific elements as nb ta ga hf th zn sn whereas f excludes ba and sr we use principal component analyses to split the granite into chemical groups allowing an unbiased study of the inter group element distribution this adds the heavy rees and y to the earlier lists of elements with an affinity for f the light rees show a decreasing affinity with decreasing atomic mass fluorine separates sm from nd whereas zr follows la opposite to some but in accordance with other earlier results the ratio nb ta is higher in the fluorite enriched than in the other granite weak tetrad effects are present zircon in the hypersolvus granite is high in common lead we suggest f to be instrumental for separating pb 2 from pb 4 two hypotheses may explain the occurrence of the two contrasting granites they have either different sources or they are co magmatic but the magma was split into two discrete types we apply the second hypothesis as our working hypothesis the liquidus has a gentler slope with pressure than the diapir requiring crystallisation to be most important in the lower part of the magma chamber our hypothesis suggests that globules of magma enriched in volatile components form during crystallisation due to slow diffusion rates in the crystallizing magma elements accompanying f are distributed into this magma batch which has a lowered density and viscosity than the rest of the magma due to its increased contents of volatile components a mushroom formed diapir rises forming the hypersolvus or almost plagioclase free granite due to an edge effect it is concentrated close to the wall of the magma chamber the size and form of the outcropping granite depend on the intersection of the diapir with the erosion surface fluorine only makes it possible to follow the process the model may be generalised to explain the diversification of non f enriched granite since the buoyancy of a magma batch several thousand m 3 in size has a much larger impact on the system than the small negative buoyancy of crystals or small crystal aggregates a type granite classified merely from its trace element content may form from separated f enriched magma batches this may be the reason for their high frequency in the eastern desert

crystallization experiments on a gusev adirondack basalt composition until recently the snc meteorites represented the only source of information about the chemistry and petrology of the martian surface and mantle the mars exploration rovers have now analyzed rocks on the martian surface giving additional insight into the petrology and geochemistry of the planet the adirondack basalts analyzed by the mer spirit in gusev crater are olivine phyric basaltic rocks which have been suggested to represent liquids and might therefore provide new insights into the chemistry of the martian mantle experiments have been conducted on a synthetic humphrey composition at upper mantle and crustal conditions to investigate whether this composition might represent a primary mantle derived melt the humphrey composition is multiply saturated at 12 5 kbar and 1375 c with olivine and pigeonite a primary anhydrous melt derived from a chondritic mantle would be expected to be saturated in orthopyroxene not pigeonite in addition the olivine and pigeonite present at the multiple saturation are too ferroan to have been from a martian mantle as is understood now therefore it seems likely that the humphrey composition does not represent a primary anhydrous melt from the martian mantle but was affected by mineral melt fractionations at lower crustal pressures

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

chronology of sand ridges and the late quaternary evolution of the etosha pan namibia abstract etosha pan situated at the southern border of tropical africa is a vast endorheic plain in namibia s semi arid north the most recent studies agree that the pan was the floor of a former lake with varying water levels here we explored this idea further by investigating the link between lake level change and records of late pleistocene and holocene climate change the varying lake levels were inferred through sediment analysis and optical dating of sand deposits that form ridges parallel to the current shore along the northern and western margins of the pan our results support the view that the sand ridges are shoreline deposits of an evaporitic lake the ridges result from the interplay between intermittent river discharge and riverine sediment supply from the north prevailing north easterly wind and shore parallel waves therefore they are a proxy for former levels of a perennial lake we infer higher levels during the late pleistocene and a drastic drop shortly after 10 ka since around 8 ka etosha pan was covered by a shallow water body this lake water level reconstruction is not in line with the histories of itcz migration and strength of benguela current upwelling we confirm that the linkages between the evolution of the etosha pan and the climate mechanisms driving hydrological changes in subtropical southwest africa are poorly resolved and need further investigation

solidus and liquidus profiles of chondritic mantle implication for melting of the earth across its history abstract we investigated the melting properties of a synthetic chondritic primitive mantle up to core mantle boundary cmb pressures using laser heated diamond anvil cell melting criteria are essentially based on the use of x rays provided by synchrotron radiation we report a solidus melting curve lower than previously determined using optical methods the liquidus curve is found between 300 and 600 k higher than the solidus over the entire lower mantle at cmb pressures 135 gpa the chondritic mantle solidus and liquidus reach 4150 150 k and 4725 150 k respectively we discuss that the lower mantle is unlikely to melt in the d layer except if the highest estimate of the temperature profile at the base of the mantle which is associated with a very hot core is confirmed therefore recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra low velocity zones indicate either 1 a outer core exceeding 4150 k at the cmb or 2 the presence of chemical heterogeneities with high concentration of fusible elements our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion not only complete melting of the lower mantle would require excessively high temperatures but also below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought in addition magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 gpa as suggested by siderophile metal silicate partitioning data such high surface temperature regime where thermal blanketing is inefficient points out to a transient character of the magma ocean with a very fast cooling rate

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

reconstruction of se trade wind intensity based on sea surface temperature gradients in the southeast atlantic over the last 25 kyr 1 a prominent feature in the southeast atlantic is the angola benguela front abf the convergence between warm tropical and cold subtropical upwelled waters at present the sea surface temperature sst gradient across the abf and its position are influenced by the strength of southeasterly se trade winds here we present a record of changes in the abf sst gradient over the last 25 kyr variations in this sst contrast indicate that periods of strengthened se trade wind intensity occurred during the last glacial maximum the younger dryas and the mid to late holocene while heinrich event 1 the early part of the bolling allerod and the early holocene were periods of weakened se trade winds

forcing of wet phases in southeast africa over the past 17 000 years a continuous record of hydrologic variability for the past 17 000 years at the mouth of the zambezi river shows that hydrologic conditions in southeast africa were controlled by variations in local insolation and migrations of the intertropical convergence zone rather than by indian ocean temperature records of hydroclimatological variability in southern africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote northern hemisphere and the more local indian ocean this paper presents a continuous record of hydrological variability for the past 17 000 years from marine sediment core drilled off the mouth of the zambezi river the record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone which were probably driven by events in the northern hemisphere rather than the indian ocean intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast africa since the last glacial maximum about 20 000 years ago in particular the relative importance of atmospheric and oceanic processes is not firmly established1 2 3 4 5 southward shifts of the intertropical convergence zone itcz driven by high latitude climate changes have been suggested as a primary forcing2 3 whereas other studies infer a predominant influence of indian ocean sea surface temperatures on regional rainfall changes4 5 to address this question a continuous record representing an integrated signal of regional climate variability is required but has until now been missing here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro climatology in southeast africa during rapid climate changes over the past 17 000 years our results are based on a reconstruction of precipitation and river discharge changes as recorded in a marine sediment core off the mouth of the zambezi river near the southern boundary of the modern seasonal itcz migration indian ocean sea surface temperatures did not exert a primary control over southeast african hydrologic variability instead phases of high precipitation and terrestrial discharge occurred when the itcz was forced southwards during northern hemisphere cold events such as heinrich stadial 1 around 16 000 years ago and the younger dryas around 12 000 years ago or when local summer insolation was high in the late holocene that is during the past 4 000 years

trace element geochemistry and genesis of precambrian sub alkaline mafic dikes from the central indian craton evidence for mantle metasomatism abstract precambrian mafic dikes transect the archaean granite gneisses of the southern bastar craton central india on the basis of high field strength elements the bastar mafic dike swarms were sub divided into an earlier bd1 and a later bd2 system the bd1 set comprises amphibolites whereas the bd2 set consists of dolerites metadolerites on the basis of field relationships and available age data for enveloping granite rocks the bd1 dikes are regarded as middle archaean in age and bd2 dikes are paleoproterozoic 1 8 ga the silica and total alkalis contents of dikes of both swarms classified them mostly as sub alkaline basalts the bd1 dikes are low ti fe and high mg olivine to quartz normative rocks whereas the bd2 dikes are predominantly quartz normative with relatively high ti fe and low mg contents the high field strength element concentrations are relatively higher in the bd2 dikes than in the bd1 dikes for comparable values of mgo and or cr judging from the geochemical data these dikes probably were not contaminated by crustal components the geochemistry and field observations clearly suggest a continental rift environment for the emplacement of both bd1 and bd2 dikes rare earth element patterns and compatible incompatible trace element modelling suggest that the two swarms were derived from distinctly different sub alkaline basaltic magmas the middle archaean bd1 dikes were derived from 15 20 batch melting of a depleted lherzolite mantle source in contrast the paleoproterozoic bd2 dikes were derived from 7 10 batch melting of a relatively enriched mantle source a post archaean increase in the thickness of metasomatized mantle lithosphere is the probable cause of mantle enrichment

turbulent metal silicate mixing fragmentation and equilibration in magma oceans abstract much of the earth was built by high energy impacts of planetesimals and embryos many of these impactors already differentiated with metallic cores of their own geochemical data provide critical information on the timing of accretion and the prevailing physical conditions but their interpretation depends critically on the degree of metal silicate chemical equilibration during core mantle differentiation which is poorly constrained efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal silicate mass transfer here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment with fragmentation into droplets eventually resulting from the entrainment process in our experiments fragmentation of the dense fluid occurs after falling a distance equal to 3 4 times its initial diameter at which point a sizable volume of ambient fluid has already been entrained and mixed with the dense falling fluid contrary to previous assumptions we demonstrate that fragmentation of the metallic phase into droplets may not be required for efficient equilibration turbulent mixing by drastically increasing the metal silicate interfacial area may result in fast equilibration even before fragmentation efficient re equilibration is predicted for impactors of size small compared to the magma ocean depth in contrast much less re equilibration is predicted for large impacts in situations where the impactor core diameter approaches the magma ocean thickness

reassessment of carbonate ages by dating both carbonate and organic material from an etosha pan namibia stromatolite evidence of humid phases during the last 20ka abstract previous research on lacustrine stromatolites from etosha pan in namibia obtained ages on carbonate close to or beyond the limits of radiocarbon dating these ages suggested that the basin was likely not subject to extensive flooding during the last ca 40 ka this study shows that ams radiocarbon ages for the carbonate of a stromatolite from poacher s point are 15 21 ka older than ages for organic material in the stromatolite structure calibrated ages range from 30 to 40 ka for carbonate and 3 19 ka for the organic residue the new ages together with petrographic and isotopic data for the stromatolite have provided important new information on past flooding of etosha pan including evidence of prolonged lacustrine conditions during the holocene climatic optimum

a lake level chronology based on feldspar luminescence dating of beach ridges at tangra yum co southern tibet many lakes on the tibetan plateau exhibit strandplains with a series of beach ridges extending high above the current lake levels these beach ridges mark former lake highstands and therefore dating their formation allows the reconstruction of lake level histories and environmental changes in this study we establish a lake level chronology of tangra yum co fifth largest lake on the tibetan plateau based on luminescence dating of feldspar from 17 beach ridge samples the samples were collected from two strandplains southeast and north of the lake and range in elevation from the current shore to 140 m above the present lake using a modified post infrared irsl protocol at 170 c we successfully minimised the anomalous fading in the feldspar irsl signal and obtained reliable dating results the luminescence ages indicate three different stages of lake level decline during the holocene 1 a phase of rapid decline 50 m from 6 4 to 4 5 ka 2 a period of slow decline between 4 5 and 2 0 ka 20 m and 3 a fast decline by 70 m between 2 ka and today our findings suggest a link between a decrease in monsoonal activity and lake level decline since the early holocene

geomorphological contributions to palaeolimnology on the african continent abstract article history received 19 december 2007received in revised form 5 july 2008accepted 22 july 2008available online 3 august 2008keywords quaternarybeach ridgeshorelinelakemultiproxyosl lakes are highly informative repositories of information of the terrestrial response to regional and global climatedrivers in quaternary studies lake oor records are now frequently used to establish the magnitude timing andgeographicalextentofhumid aridtransitionsovertimescalesof10 2 10 4 years whiletheresolutionof thisrecordisunparalleled much of the geochemical and sedimentary da ta is challenging to interpret and highly basin speci c geomorphologicalproxies particularlyshorelines offeranadditionaloralternativerecordoflakehistory withrecenttechnological advances facilitating both access to and the utility of this proxy record recent advances in opticallystimulated luminescence osl dating allow the determination of the age of beach ridge emplacement in theabsence of organic material while the availabilityof shuttle radar topography mission srtm data in conjunctionwith digital elevation models dem aids in the identi cation of shoreline features and the topographicreconstruction of the former extent of palaeolakes here we highlight and illustrate the use of lacustrine shorelinefeatures for unravelling a quaternary climate signal wit hin africa from otherwise inaccessible and undatablepalaeolake records in the semi arid and arid subtropics an d identify their contribution towards high resolutionmultiproxy reconstructions of tropical low latitude quaternary environments and climates 2008 elsevier b v all rights reserved

are discontinuous chondrite normalized ree patterns in pegmatitic granite systems the results of monazite fractionation abstract all 14 stable rare earth elements rees in biotite muscovite granite and tourmaline rich granite of the harney peak granite black hills south dakota usa have been analyzed using inductively coupled plasma mass spectrometry chrondrite normalized ree patterns of the tourmaline rich granites are discontinuous between nd and sm the discontinuity was modeled successfully by the fractional crystallization of monazite from a biotite muscovite granite initial composition this explanation may also apply to the development of such discontinuous patterns in other highly evolved rocks

tetrad effect in rare earth element distribution patterns a method of quantification with application to rock and mineral samples from granite related rare metal deposits abstract in some geological environments the tetrad effect can be observed as a split of rare earth element ree patterns into four rounded segments a new method is proposed to quantify the sizes of the individual segments and for the first time the significance of observed tetrad effects is evaluated by taking analytical errors into account the outlined method was applied to lanthanide patterns of whole rock and fluorite samples collected from granite related rare metal deposits the ree patterns of the granite and greisen samples investigated exhibit significant tetrad effects that may not be accounted for by analytical uncertainties it is shown that the study of whole rock samples is insufficient to determine whether this effect is developed during fractional crystallization or is due to other processes such as fluid rock interaction a concave tetrad effect mirroring the pattern of the whole rock samples was not observed in the ree patterns of related vein fluorite samples therefore it is unlikely that the convex tetrad effect in the samples from the magmatic environment can be explained by removal of a respective complementary ree pattern by a coexisting hydrothermal fluid as previously suggested it is proposed that the tetrad effect formed within the magma fluid system before emplacement in the subvolcanic environment where phase separation caused a split of this system into fluid and magma subsystems alternatively the tetrad effect may also be inherited from an external fluid influencing the system during or after the emplacement of the magma on the basis of the fluorite data it is shown that the behavior of eu in the fluids is not related to the tetrad effect consequently different physico chemical factors control the occurrence of both phenomena y was found to be strongly enriched in samples precipitating from hydrothermal fluids that experienced prolonged interaction with the wall rocks whereas the tetrad effect in the fluids vanished with time and increasing distance from the ore bearing granite thus these different geochemical parameters can be used to reconstruct different aspects of the fluid evolution within this type of deposit

valence and metal silicate partitioning of mo implications for conditions of earth accretion and core formation abstract to better understand and predict the partition coefficient of mo at the conditions of the deep interior of earth and other terrestrial planets or bodies we have undertaken new measurements of the valence and partitioning of mo x ray absorption near edge structure xanes k edge spectra for mo have been measured in a series of fe bearing glasses produced at 1 bar and higher pt conditions high pressure experiments have been carried out up to 19 gpa in order to better understand the effect of pressure on mo partitioning and finally a series of experiments at very low f o 2 conditions and high si content metallic liquids has been carried out to constrain the effect of si on the partitioning of mo between metallic liquids and silicate melt the valence measurements demonstrate that mo undergoes a transition from 4 to 6 near iw 1 in general agreement with previous 1 bar studies on feo free silicate melts high pressure experiments demonstrate a modest pressure dependence of d mo metal silicate and combined with previous results show a significant decrease with pressure that must be quantified in any predictive expression finally the effect of dissolved si in fe rich metallic liquid is to decrease d mo significantly as suggested by previous work in metallurgical systems the effect of pressure temperature oxygen fugacity metallic liquid composition and silicate melt composition can be quantified by using multiple linear regression of available experimental data for mo our xanes results show that mo will be 4 at conditions of core formation so only experiments carried out at f o 2 of iw 1 and lower were used in the regressions application of predictive expressions to earth accretion shows that d mo decreases to values consistent with an equilibrium scenario for early earth core mantle the mo content of the primitive upper mantle pum can be attained by metal silicate equilibrium involving s c and si bearing metallic liquid and peridotite silicate melt along the peridotite liquidus near 45 gpa and 3600 c late in the accretion process this conclusion is insensitive to late giant impacts unless the degree of equilibration is very low

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

an early proterozoic leuco granitic gneiss with the ree tetrad phenomenon abstract we report here the occurrence of a peculiar leuco granitic gneiss in the imweon area in south korea the chondrite normalized rare earth element ree patterns of this leuco granitic gneiss and its constituent minerals exhibit the tetrad phenomenon which suggests a special event related to aqueous activity in addition the sm 1bnd internal isochron for the whole rock and its constituent minerals gives an age of 2250 4 ma with an initial ratio of 0 50942 0 00002 nd 5 7 these facts suggest that there should be an environment to give rise to the ree tetrad phenomenon in the crust 2 25 ga ago such an environment may be produced by the water phase resulting from anatexis or the fluid phase in the source material itself before anatexis subsequent to the stage where the ree content was lowered due to prolonged fluid circulation throughout the granitic melt the eu depletion compared to the ree the ree redistribution among constituent minerals and the tetrad phenomenon are considered to be cognate even if there had been some time lags between the responsible steps

the behaviour of rees in thailand s mae klong estuary suggestions from the y ho ratios and lanthanide tetrad effects abstract the concentrations of rare earth elements and yttrium rey were measured in dissolved phase in suspended particulate matter spm and in sediments in seven sampling stations in the mae klong estuarine system inner thailand gulf in order to study their behaviour and distribution pattern the analysed samples generally show high rare earth element ree content in the dissolved phase with high medium rare earth elements mrees and y enrichments in the shale normalized pattern versus paas these chemical features are interpreted in terms of direct influences of weathering processes of ree rich minerals e g phosphates which abundantly out crop in the mae klong watershed these large mree enrichments also suggest that dissolved sulphate complexes play an important role in the dissolved ree fate close to the marine coastal system the shale normalized rees and y ho ratios additionally indicate a direct rey co precipitation with fe oxyhydroxides along the river path and consequent adsorption as coating onto feooh surfaces the rey behaviour in spm appears strongly influenced by al fe and mn content suggesting that the formation of an authigenic fe mn oxyhydroxides and aluminosilicate particulate leads to rey adsorption and or co precipitation the observed variations in the y ho ratios suggest that different y ho fractionation processes take place in the studied estuarine system strong similarities among chondrite normalized ree patterns in both sediments and granitic rocks out cropping in the surrounding regions suggest a generic relationship between the two groups of materials

the response of the walker circulation to last glacial maximum forcing implications for detection in proxies 1 the response of the walker circulation to last glacial maximum lgm forcing is analyzed using an ensemble of six coordinated coupled climate model experiments the tropical atmospheric overturning circulation strengthens in all models in a manner that is dictated by the response of the hydrological cycle to tropical cooling this response arises from the same mechanism that has been found to explain the weakening of the tropical circulation in response to anthropogenic global warming but with opposite sign analysis of the model differences shows that the ascending branch of the walker circulation strengthens via this mechanism but vertical motion also weakens over areas of the maritime continent exposed due to lower sea level each model exhibits a different balance between these two mechanisms and the result is a pacific walker circulation response that is not robust further even those models that simulate a stronger walker circulation during the lgm do not simulate clear patterns of surface cooling such as la nina like cooling or enhanced equatorial cooling as proposed by previous studies in contrast the changes in the walker circulation have a robust and distinctive signature on the tilt of the equatorial thermocline as expected from zonal momentum balance the changes in the walker circulation also have a clear signature on the spatial pattern of the precipitation changes a reduction of the east west salinity contrast in the indian ocean is related to the precipitation changes resulting from a weakening of the indian walker circulation these results indicate that proxies of thermocline depth and sea surface salinity can be used to detect actual lgm changes in the pacific and indian walker circulations respectively and help to constrain the sensitivity of the walker circulation to tropical cooling

origin and evolution of uraniferous pegmatite a case study from the xiaohuacha granite pegmatite system and related country rocks in the shangdan uranium mineralization district of north qinling orogenic belt china abstract the shangdan district in the north qinling orogenic belt hosts the largest pegmatite type uraniferous province in china the xiaohuacha u mineralization in this district occurs along the contact zone between biotite pegmatite and its host rock of biotite gneiss adjacent to the composite huichizi batholith which is composed mainly of biotite monzogranite and syenogranite zircon u pb dating of these granitoids reveals two stage magmatism namely the early silurian for biotite monzogranite 438 5 4 4 ma and the early devonian for syenogranite 417 8 3 2 ma the biotite pegmatite shows an age of 415 8 3 8 ma for the mineralized marginal zone and similar ages of 414 6 4 3 ma and 413 2 3 5 ma are obtained for the barren marginal and intermediate zones respectively the biotite monzogranite exhibits a restricted range of positive zircon ehf t values of 5 3 to 7 8 with tdm2 ages of 0 93 1 08 ga suggesting magma derivation from mainly pre existing basaltic rocks in the orogenic root magmatic oxygen fugacity fo2 was estimated by ti in zircon thermometry and ce incorporation within zircons the biotite monzogranite was emplaced at a temperature of 736 24 c with log fo2 values of 22 28 to 14 19 in contrast the syenogranite zircons have ehf t values of 1 4 to 2 4 and tdm2 ages of 1 25 1 49 ga indicating a derivation from the mesoproterozoic crust with some mantle input pristine zircon domains from different zones of the biotite pegmatite display ehf t values of 2 8 to 1 8 and tdm2 ages of 1 29 1 58 ga similar to those of the syenogranite indicating they share a common magma source combination of petrographical geochronological isotopic and mineral chemical data supports a petrogenetic relationship between the high t 842 14 c syenogranite and biotite pegmatite 756 21 c and 709 26 c for the uncontaminated marginal and intermediate zones respectively through magmatic differentiation from the same magma source during a period of tectonic extension processes of segregation and emplacement of the pegmatitic magma are consistent with open system assimilation and fractional crystallization afc leading to decreasing log fo2 values from the syenogranite 11 23 to 7 02 to biotite pegmatite through a fractionation trajectory however log fo2 values increase from the uncontaminated pegmatite marginal 15 88 to 10 9 to intermediate 17 86 to 6 14 zones with closed system pegmatite internal evolution the interaction hybridization between magma and gneiss induced decrease of oxidation state and k na al as well as modifications to zircon compositions in the mineralized pegmatite marginal zone we propose a model with decreasing of fo2 and k na al during afc being the main controls on the formation of the u deposit

the effect of melt composition on metal silicate partitioning of siderophile elements and constraints on core formation in the angrite parent body we present 275 new metal silicate partition coefficients for p s v cr mn co ni ge mo and w obtained at moderate p 1 5 gpa and high t 1683 1883 k we investigate the effect of silicate melt composition using four end member silicate melt compositions we identify possible silicate melt dependencies of the metal silicate partitioning of lower valence elements ni ge and v elements that are usually assumed to remain unaffected by changes in silicate melt composition results for the other elements are consistent with the dependence of their metal silicate partition coefficients on the individual major oxide components of the silicate melt composition suggested by recently reported parameterizations and theoretical considerations using multiple linear regression we parameterize compiled metal silicate partitioning results including our new data and report revised expressions that predict their metal silicate partitioning behavior as a function of p t x fo2 we apply these results to constrain the conditions that prevailed during core formation in the angrite parent body apb our results suggest the siderophile element depletions in angrite meteorites are consistent with a cv bulk composition and constrain apb core formation to have occurred at mildly reducing conditions of 1 4 0 5 log units below the iron wustite buffer iw corresponding to a apb core mass of 18 11 the core mass range is constrained to 21 8 mass if light elements s and or c are assumed to reside in the apb core incorporation of light elements in the apb core does not yield significantly different redox states for apb core mantle differentiation the inferred redox state is in excellent agreement with independent fo2 estimates recorded by pyroxene and olivine in angrites

quantifying trace element disequilibria in mantle xenoliths and abyssal peridotites we apply a tool based on element distribution between orthopyroxene and clinopyroxene for quantifying rare earth element ree disequilibria in ultramafic rocks in the subsolidus state we present case studies of the ree contents of mineral cores in mantle xenoliths and abyssal peridotites using in situ analytical tools even when only mineral cores are measured to avoid enriched rims equilibrium is not always achieved on the mineral scale mineral cores in mantle xenoliths are closer to equilibrium than those in abyssal peridotites even though mantle xenoliths are known to be light ree contaminated from the host lava in the case of the abyssal peridotites 13 out of 14 are out of equilibrium with the least metasomatized most in disequilibrium and the most metasomatized closest to equilibrium we discuss hypotheses for these observations but regardless of what caused the disequilibria this tool allows one to see through the effects of secondary processes such as infiltration by fluid inclusions via cracks and diffusive exchange between minerals and melts fluids along grain boundaries the ease of making in situ ree measurements makes this tool formidable in identifying different generations of clinopyroxenes in ultramafic lithologies such data will complement the interpretation of isotopic and petrographic studies of continental and oceanic lithospheric mantle

fluid inclusions and rare earth element geochemistry of fluorite from south central idaho epithermal fluorite mineralization of tertiary age occurs in a northeast trending belt within the challis 2 degrees quadrangle of south central idaho fluorite was collected from the meyers cove area and the bayhorse yankee fork and stanley mining districts host rocks include the eocene challis volcanics the cretaceous idaho batholith and the ordovician bayhorse dolomite mineralization is structurally controlled and is present as fault and fracture fillings and breccia cements argillization and silicification of the wall rocks is common and locally intense microthermometric measurements on nearly 400 two phase h 2 o vapor water rich inclusions with low vapor to liquid ratios yielded mean homogenization temperatures of 160 degrees c for the meyers cove area 150 degrees c for the stanley district and 130 degrees c for the bayhorse and the yankee fork districts salinities range from 0 to 1 4 equiv wt percent nacl the rare earth element content of the fluorite is quite variable ranging from 2 6 to 130 ppm and ce yb ratios reflect the dominant trend of light rare earth element enrichment fluorite from the meyers cove area and the bayhorse and stanley districts have similar tb la ratios indicating crystallization at about the same time fluorite from the yankee fork district has a lower mean tb la ratio which is indicative of earlier crystallization chondrite normalized plots and rare earth element ratios reveal persistent negative ce anomalies indicating high oxygen fugacities at the source area positive eu anomalies indicate the release of eu super 2 during feldspar destruction oxidation to eu super 3 at the deposition site and subsequent incorporation in the fluorite samples with negative eu anomalies indicate the presence of divalent eu the fluid inclusion geochemical geologic geochronologic and stable isotope data support deposition in tertiary hydrothermal systems dominated by fluids of meteoric origin the most important depositional mechanism is believed to be an increase in the ph of the ore bearing fluids upon interaction with the wall rocks

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

comparative geochemical study of scheelite from the shizhuyuan and xianglushan tungsten skarn deposits south china implications for scheelite mineralization abstract scheelite has been analyzed from the shizhuyuan and the xianglushan world class w deposits from the nanling w sn region and jiangnan w belt respectively the shizhuyuan deposit consists of proximal skarn and greisen w sn mo bi and distal pb zn ag veins the xianglushan deposit contains layer like sulfide scheelite and skarn w orebodies on granite cupolas overprinted by w greisen veins scheelite in skarn ores from the shizhuyuan contains higher concentrations of mo than those in the sulfide scheelite and skarn ores from the xianglushan deposit reflecting differences between oxidizing and reducing magmatic hydrothermal fluids under oxidizing conditions w is accompanied by mo partitions into exsolved fluids to form w mo garnet skarns whereas under reducing conditions little mo is carried by exsolved fluids to form w pyroxene skarns trace element patterns of scheelite from both deposits show negative ba sr zr and ti and positive ta anomalies rare earth element ree patterns of scheelite within skarns from the shizhuyuan deposit have negatively inclined and flat m type tetrad patterns and scheelite from the greisens displays flat and positively inclined m type tetrad patterns we infer that the fluids formed scheelite within the w skarns and greisens inherited parental magma trace element and ree characteristics depleted ba sr zr and ti enriched ta negative eu anomalies and tetrad effects whereas scheelite from sulfide scheelite veins and skarns of the xianglushan deposit also has w and mw type tetrad ree patterns the w type tetrad ree patterns are complementary to ree patterns from the renjiashan granite and the mw type tetrad ree patterns occur during a single evolutionary stage within a complex hydrothermal environment sulfide mineralization can form after or before w skarns the former like shizhuyuan deposit and the latter like xianglushan deposit the formation conditions of the latter included reducing conditions and sulfide firstly supersaturated in the melt resulting in sulfide drops which carried w aggregated on the cupolas w skarns and greisens in both deposits underwent generally successive processes related to water supersaturation in the melt following a temperature decrease and crystallization bubbles carried material changing from si and metal to si oxide complexes

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

fluid inclusions muscovite ar ar age and fluorite trace elements at the baiyanghe volcanic be u mo deposit xinjiang northwest china implication for its genesis abstract the baiyanghe be u mo deposit is located in the late paleozoic xuemisitan kulankazi island arc of the northwestern margin of the junggar plate northwest china it is the largest be deposit 2 2 m tons of ore with grades ranging from 0 2 to 1 4 in asia orebodies in the deposit occur as fractures along contact zones between the yangzhuang granite porphyry intrusion and devonian pyroclastic country rocks and within the porphyry itself muscovite fluorite veins are closely associated with the be u mo mineralization a new ar ar dating of the muscovite in this study yields a plateau age of 303 0 1 6 ma which constrains the timing of the be u mo mineralization of the deposit three stages of fluorite of different colors have been identified at the deposit with the earliest dark purple fluorite more closely associated with the mineralization microthermometry of fluid inclusions obtained from the three stages of fluorite suggests that the fluorites were precipitated as veins from low temperature 120 150 c hydrothermal fluids with salinity ranging from 4 7 to 19 7 wt nacl eqv based on the trace elemental concentrations and ree patterns of the fluorite the style of veining and the low salinity and low temperature characters of the fluid inclusions it is suggested that be and u were most likely transported as fluoride complexes and mo as hydroxyl complexes pb isotopic compositions of the ores and country rocks as well as o and h isotopic characters of the ore related muscovite indicate mixing between magmatic and meteoric waters both contributed to formation of the ore forming fluids metallic be u and mo were most likely leached out from the granite porphyry by the fluids the fluid mixing led to the reduction of u mo and be and their precipitation at the deposit

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

fluid regime and ore formation in the tungsten yttrium deposits of kyzyltau mongolian altai evidence for fluid variability in tungsten tin ore systems abstract the kyzyltau ore field is located in the northern part of the mongolian altai mountains w y be mo mineralization occurs in veins and stockworks in granites felsic volcanics basaltic flows and conglomerates the main ore minerals in the veins are wolframite fluorite beryl and minor molybdenite inclusions in hydrothermal quartz fluorite and beryl from veins as well as in magmatic quartz in vein hosting granites of the ulaan uul buraat uul and tsunkheg deposits were investigated using microthermometry and laser raman spectroscopy pseudosecondary primary inclusions in the kyzyltau ore veins are predominantly liquid rich aqueous inclusions containing variable amounts of co 2 as the main gas component and showing n 2 ch 4 ratios 1 secondary inclusions contain no or only trace concentrations of gases as indicated by clathrate melting the t h values of pseudosecondary primary inclusions in veins are between 180 and 433 c fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz ii and green fluorite ii in the ulaan uul and buraat uul ore veins phase separation pressures of 100 350 bars were estimated fluorite i from the kyzyltau ore field shows a strong enrichment of hree and a strong negative eu anomaly common for rare metal bearing ore systems fluorite ii from buraat uul and tsunkheg is characterized by a change in the incorporation of rare earth elements ree with decreasing hree contents and a decreasing eu anomaly the ree distribution patterns in fluorite ii from ulaan uul remained unchanged compared with fluorite i despite a strong increase in the total ree content a review of the literature shows that from high temperature fe rich k dominated brines cassiterite ores can precipitate in quartz veins together with fe chlorite and fe tourmaline bolivian type if phase separation of a gas rich low salinity and fe rich fluid occurs cassiterite wolframite ores may be deposited cornwall devon type the deposits of kyzyltau are characterized by low fe alteration assemblages a predominance of sodium over potassium high contents of ree and y and a lack of extended tin mineralization despite the tin potential of the ore systems fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of li f rich sub volcanic intrusions we interpret the ph of the mineralizing fluid to be the main factor controlling wolframite precipitation in the kyzyltau ore field fluid wall rock interactions a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid co 2 bearing fluid into a ph range where tungstates were precipitated it can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten according to this inference tin mineralization may be found in a more favourable setting in the vicinity of the kyzyltau deposits

the molybdenum isotopic compositions of i s and a type granitic suites this study reports mo isotopic compositions for fifty two palaeozoic granitic rocks with contrasting source affinities a i and s type from the lachlan fold belt lfb and the new england batholith neb both in se australia and three compositionally zoned plutons loch doon criffell and fleet located in the southern uplands of scotland the results show relatively large variations in 98mo for igneous rocks ranging from 1 73 to 0 59 with significant overlaps between different types no relationships between 98mo and 18o or asi alumina saturation index are observed indicating that mo isotopes do not clearly distinguish igneous vs sedimentary source types instead effects of igneous processes source mixing regional geology as well as hydrothermal activity control the mo isotope compositions in these granites it is found that mo is mainly accommodated in biotite and to a lesser extent in hornblende hornblende and fe3 rich minerals may preferentially incorporate light isotopes as reflected by negative correlations between 98mo and k rb and fe2o3 there is a positive correlation between initial 87sr 86sr and 98mo in i type granitic rocks reflecting the admixing of material from isotopically distinct sources granitic rocks from scotland and australia display strikingly similar curvilinear trends in 98mo vs initial 87sr 86sr despite the differing regional geology localized hydrothermal effects can result in low 98mo in granite as seen in three samples from loch doon and criffell which have anomalously light 98mo of 1 based on this study an estimate of 98mo 0 14 0 07 95 s e for the phanerozoic upper crust is proposed this is slightly heavier than basalts indicating an isotopically light lower crust and or a systematic change to the crust resulting from subduction of isotopically light dehydrated slab and or pelagic sediment over time

tungsten isotopic evidence for disproportional late accretion to the earth and moon examination of three lunar samples reveals that the moon s mantle has an excess of the tungsten isotope 182w of about 20 parts per million relative to the present day earth s mantle this suggests that the two bodies had identical compositions immediately following the formation of the moon and that the compositions then diverged as a result of disproportional late accretion of chondritic material to the earth and moon two papers published in this issue of nature present precise measurements of tungsten isotope composition in lunar rocks that are best explained by the earth and moon having had similar composition immediately following formation of the moon and then having diverged as a result of disproportional late accretion of material to the two bodies mathieu touboul et al found small 182w excess of about 21 parts per million relative to the present day earth s mantle in metals extracted from two kreep rich apollo 16 impact melt rocks while thomas kruijer et al measured tungsten isotopes in seven kreep rich whole rock samples that span a wide range of cosmic ray exposure ages and found a 182w excess of about 27 parts per million over the present day earth s mantle characterization of the hafnium tungsten systematics 182hf decaying to 182w and emitting two electrons with a half life of 8 9 million years of the lunar mantle will enable better constraints on the timescale and processes involved in the currently accepted giant impact theory for the formation and evolution of the moon and for testing the late accretion hypothesis uniform terrestrial mantle like w isotopic compositions have been reported1 2 among crystallization products of the lunar magma ocean these observations were interpreted to reflect formation of the moon and crystallization of the lunar magma ocean after 182hf was no longer extant that is more than about 60 million years after the solar system formed here we present w isotope data for three lunar samples that are more precise by a factor of 4 than those previously reported1 2 the new data reveal that the lunar mantle has a well resolved 182w excess of 20 6 5 1 parts per million 2 standard deviations relative to the modern terrestrial mantle the offset between the mantles of the moon and the modern earth is best explained by assuming that the w isotopic compositions of the two bodies were identical immediately following formation of the moon and that they then diverged as a result of disproportional late accretion to the earth and moon3 4 one implication of this model is that metal from the core of the moon forming impactor must have efficiently stripped the earth s mantle of highly siderophile elements on its way to merge with the terrestrial core requiring a substantial but still poorly defined level of metal silicate equilibration

a jurassic garnet bearing granitic pluton from ne china showing tetrad ree patterns abstract ne china is characterized by the massive distribution of phanerozoic granitoids most of them are of i and a type granites whereas s type granites are rarely documented the present work deals with the dongqing pluton a small granitic body emplaced in the southern zhangguangcai range the pluton comprises a two mica garnet granite and a garnet bearing muscovite granite the latter occurs as veins in the former the pluton shows a gradational contact with the surrounding host granites rb sr and sm nd isotope analyses on whole rocks and minerals reveal that the two types of granites were emplaced synchronously at about 160 ma the pluton was emplaced coeval with the surrounding i type granitic pluton and had a rapid cooling history it is characterized by an initial sr isotopic ratio of 0 706 slightly negative end t values 0 5 to 1 9 and young depleted mantle model ages 970 1090 ma this suggests that the parent magma originated from partial melting of relatively juvenile crust which is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt geochemically the granites of the dongqing pluton are peraluminous with a shand index molar ratio a cnk of 1 0 1 1 for the two mica granites and 1 2 1 3 for the garnet bearing granites all the garnet bearing granites and some of the two mica granites show tetrad ree patterns tetrad group whereas most two mica granites show normal granitic ree patterns normal group the normal group granites exhibit depletion in nb ta p and ti in spidergrams and generally weak positive eu anomalies in ree patterns by contrast the tetrad group granites manifest depletion in ba nb ta sr p and ti and significant negative eu anomalies the trace element data constrain the parental magmas to having undergone extensive magmatic differentiation during their late stage magmatic evolution intense interaction of residual melts with aqueous hydrothermal fluids resulted in the non charac charge and radius controlled trace element behavior and the tetrad effect in ree distribution patterns this in turn leads to the invalidation of the commonly used tectonic discrimination criteria derived from trace element abundances of normal granites in view of this and previous studies we conclude that there were probably no s type granites produced in ne china during the phanerozoic consequently weathered sedimentary material did not play an important role in the genesis of the strongly peraluminous granites in the zhangguangcai range

evidence for progressive holocene aridification in southern africa recorded in namibian hyrax middens implications for african monsoon dynamics and the african humid period abstract presented here are stable nitrogen isotope data from a rock hyrax procavia capensis middens from northwestern namibia that record a series of rapid aridification events beginning at ca 3800 cal yr bp and which mark a progressive decrease in regional humidity across the holocene strong correlations exist between this record and other terrestrial and marine archives from southern africa indicating that the observed pattern of climate change is regionally coherent combined these data indicate hemispheric synchrony in tropical african climate change during the holocene with similar trends characterising the termination of the african humid period ahp in both the northern and southern tropics these findings run counter to the widely accepted model of direct low latitude insolation forcing which requires an anti phase relationship to exist between the hemispheres the combined dataset highlights 1 the importance of forcing mechanisms influencing the high northern latitudes in effecting low latitude climate change in africa and 2 the potential importance of solar forcing and variations in the earth s geomagnetic shield in determining both long term and rapid centennial scale climate changes identifying a possible mechanism for the variations marking the ahp termination in both the southern and northern tropics

estimation of trace element concentrations in the lunar magma ocean using mineral and metal silicate melt partition coefficients this study uses experimentally determined plagioclase melt d values to estimate the trace element concentrations of sr hf ga w mo ru pd au ni and co in a crystallizing lunar magma ocean at the point of plagioclase flotation similarly experimentally determined metal silicate partition experiments combined with a composition model for the moon are used to constrain the concentrations of w mo ru pd au ni and co in the lunar magma ocean at the time of core formation the metal silicate derived lunar mantle estimates are generally consistent with previous estimates for the concentration of these elements in the lunar mantle plagioclase melt derived concentrations for sr ga ru pd au ni and co are also consistent with prior estimates estimates for hf w and mo however are higher these elements may be concentrated in the residual liquid during fractional crystallization due to their incompatibility alternatively the apparent enrichment could reflect the inappropriate use of bulk anorthosite data rather than data for plagioclase separates

accretion and core formation on mars molybdenum contents of melt inclusion glasses in three snc meteorites abstract molybdenum cerium barium yttrium and rubidium contents of glasses in melt inclusions in three snc meteorites lew 88516 governador valadares and chassigny have been measured by ion microprobe ratios of mo ba and mo ce have been used to estimate the mo content of the primitive martian mantle 120 60 ppb abundances of five moderately siderophile elements ni co mo w and p and re in the martian mantle are consistent with metal silicate equilibrium between s bearing metallic liquid in a core 22 wt of the planet and peridotite melt at 75 kb 1620 c and oxygen fugacity 1 4 logfo2 units below the iw buffer this homogeneous accretion scenario is different than many heterogeneous accretion models for the earth but similar to recent studies suggesting homogeneous accretion in the presence of a deep terrestrial magma ocean

tologoi key section a unique archive for pliocene pleistocene paleoenvironment dynamics of transbaikalia bikal rift zone abstract the multi layered key section of tologoi is situated on the selenga river left bank 15 km southwest of ulan ude city 51o45 n 107o29 e in the western transbaikal region it holds a long record of quaternary sedimentation since early late pliocene through holocene with the only minor gap in the beginning of early pleistocene comprehensive studies have been carried out on the lithology geochemistry fauna succession and paleoenvironment reconstructions this paper summarizes the data acquired on the geology and stratigraphy of the tologoi section the authors investigated the composition structure and formation conditions of the section as well as the intensity of weathering rock geochemistry grain size and biostratigraphy

rare earth element geochemistry of sulphide weathering in the sao domingos mine area iberian pyrite belt a proxy for fluid rock interaction and ancient mining pollution gossan disseminated orebody waste other mining wastes minesoils and acid mine drainage amd in the abandoned sao domingos mine area iberian pyrite belt ipb have been analyzed for rare earth elements ree the main aim is to understand ree mobility during sulphide weathering so that the lanthanide series can be used both as a record of the water rock interaction and as a tool for identifying impacts of amd on natural ecosystems north american shale composite nasc normalized ree patterns corresponding to the disseminated orebody waste are relatively flat emree 0 01 0 12 however nasc normalized ree distributions in amd from sulphide oxidation tend to be enriched in middle ree mree compared to light ree lree and heavy ree hree as a consequence gossan resulting from supergene alteration of massive sulphide presents an evident nasc normalized mree depleted signature thus the overall water sulphide interaction defines complementary convex emree 0 72 0 25 and concave emree 0 31 0 12 nasc normalized patterns in draining waters and oxidation products respectively solutions extracted from minesoils have also nasc normalized patterns with mree enriched signature emree 0 62 0 22 similar to amd the emree parameter is proposed to measure the curvature in the mree segment and its size is quantified as the normalized maximum vertical difference between the polynomial curve fitting of the mree region and its theoretical y axis position in the absence of enrichment or depletion emree 0 for mree enriched signatures 0 for mree depleted signatures and 0 for horizontal patterns the sao domingos stream although it has been highly affected by amd flows into the guadiana river that has an estuarine system where pollution is considerably attenuated due to the mixing according to the metal geoaccumulation indexes currently used in the literature however sediments of this estuary were also analyzed and reflect mree enriched signatures emree 0 25 0 03 which demonstrate that this apparently non polluted estuarine system is being certainly affected by historical mining activities from the ipb the emree index is more sensitive to recognize curved mree signatures than other normalized ratios such as la gd nasc validating the use of ree patterns as a proxy for environmental pollution by amd

the influence of silicate melt composition on distribution of siderophile elements among metal and silicate liquids abstract liquid metal liquid silicate partitioning of fe ni co p ge w and mo among a carbon saturated metal and a variety of silicate melts magnesian tholeiitic siliceous aluminous aluminosiliceous basalts depends modestly to strongly upon silicate melt structure and composition low valency siderophile elements fe ni and co show a modest influence of silicate melt composition on partitioning germanium shows a moderate but consistent preference for the depolymerized magnesian melt high valency siderophile elements p mo and w show more than an order of magnitude decrease in metal silicate partition coefficients as the silicate melt becomes more depolymerized detailed inspection of our and other published w data shows that polymerization state temperature and pressure are more important controls on w partitioning than oxidation state for this to be true for a high and variable valence element implies a secondary role in general for oxidation state even though some role must be present equilibrium core segregation through a magma ocean of ultrabasic composition can provide a resolution to the excess abundances of ge p w and mo in the mantle but the mantle composition alone cannot explain the excess abundances of nickel and cobalt in chondritic proportions

grain size variation on dunes in the southwest kalahari southern africa abstract grain size parameters mean standard deviation skewness and kurtosis were determined for 83 sediment samples from six dune cross profiles and one 28 km long profile on dunes in the southwest kalahari desert in southern africa although some studies elsewhere and previous studies in the kalahari have reported significant grain size variation over dune cross profiles data presented here show no systematic variation of grain size parameters except that sediments from the crest of a dune are almost invariably better sorted indicated by the standard deviation of the sample than samples from the base or plinth of the dune the proportion of fines 63 m in plinth sediments is also greater than in crest samples there is no significant trend in grain size parameters along the length of a linear dune this lack of significant pattern corresponds with similar findings for central australian dunes

genetically related mo bi ag and u f mineralization in a type granite gabal gattar eastern desert egypt abstract molybdenum bismuth silver and uranium fluorine mineralization in the gabal gattar area are genetically related both are hosted in fractionated and hydrothermally altered a type granite while mo bi ag ore is hosted in ns striking quartz veins the u f mineralization forms batches and micro veinlets controlled by nne to nw trending structures u was incorporated in late magmatic hypogene minerals e g zircon and xenotime and in u th minerals closely associated with fluorite molybdenite native bismuth galena chalcopyrite sphalerite aikinite pbcubis 3 berryite s 16 cu ag 6 bi 7 pb 3 and native silver were identified in the quartz veins fluid inclusions occur in fluorite type 1 associated with u minerals and in quartz type 2 from mo bearing veins type 1 and 2 inclusions homogenize at temperatures between 220 c and 106 c their salinity ranges from 1 3 to 10 wt nacleq respectively f rich fluids accumulated at the last stage of granite crystallization extracted ore metals and deposited them in a shallow hydrothermal system mo bi and ag precipitated earlier from saline fluids due to cooling fluid mixing and wallrock sulfidation u f minerals precipitated from low salinity fluids after high input of meteoric water

assessment of drainage network extractions in a low relief area of the cuvelai basin namibia from multiple sources lidar topographic maps and digital aerial orthophotographs abstract accurate delineation of drainage networks dns is crucial for hydrological or hydraulic modelling and the comprehension of fluvial processes this task presents challenging aspects in complex lowland terrains with subtle relief and particularly for data poor areas like the cuvelai river basin crb namibia where the present study takes place in the crb standard methods of drainage network extraction from low resolution gridded digital elevation models dems are unsuitable hence airborne light detection and ranging lidar solutions have been utilized however lidar also presents challenges to large areal applications especially with a surface roughness exceeding the capacity of numerous algorithms indeed lidar based dems 2 and 50 m resolutions need to be hydrologically corrected and smoothed to enable the extraction of scale relevant geomorphologic features such as dns in the present contribution channels from topographic maps blue lines were compared to those from hydrologically corrected and uncorrected lidar dems heads up digitized channels from high resolution digital aerial orthophotographs field mapped channels and auxiliary data the maximum gradient deterministic eight d8 gis algorithm was applied to the corrected and uncorrected lidar dems using two network extraction methods area threshold support and curvature drop analysis different progressive flow accumulation threshold values 12 were used to delineate channels with these methods validation was performed between the field mapped channels the modelled channels and those derived from multiple sources additionally spatial and quantitative analyses were performed on geomorphologic parameters and indices the results have shown that hydrologically corrected lidar dems offer useful details for identifying low order stream segments in headwaters while blue lines derived from the national hydrography datasets for watersheds located in elevated and low lying areas of the study area underestimated total stream lengths for field mapped channels by 15 3 and 88 5 respectively this study also confirmed that dns can be extracted from complex low terrain areas with standard gis algorithms and accurate field data the results will aid national mapping agencies in data poor regions to modernize their national hydrography datasets and to account for changing land surface conditions that can affect channel spatial arrangements over time

grain size characteristics of linear dunes in the southwestern kalahari abstract linear dunes in the southwestern kalahari sand sea exhibit characteristic grain size and sorting patterns in which sands become coarser better sorted and more finely skewed from interdune to crest in addition at a regional scale sands tend to become finer and better sorted in the direction of transport these patterns can best be explained in terms of the differential movement of sand in creep and saltation populations whereby the saltating population moves more rapidly and is concentrated downwind and in dunes slower moving creep populations remain close to source areas and in interdunes the fines will tend to be concentrated in interdunes because they can penetrate between coarse grains where they are protected from further movement this type of model probably explains most grain size and sorting relationships in desert sand seas

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

a geochemical study of loess and desert sand in northern china implications for continental crust weathering and composition abstract chemical compositional variations of desert sands and loess loess like deposits river deposits and saline lacustrine deposits collected mostly from the southern margin of the taklimakan desert china provide strong constraints on the chemical weathering processes of continental crust and also on the provenance compositions of these quaternary deposits constant but lower concentrations of al relative to the average upper continental crust ucc in these quaternary deposits could be attributed to chemical weathering of al rich minerals such as feldspar and mica and removal of clay minerals by wind and water large variations of mobile na ca mg and sr compared to relatively immobile al k and ba resulted from the chemical weathering of plagioclase and carbonate minerals salinization and carbonation of the arid lands most trace elements are not significantly fractionated their variations in absolute concentration are caused by the dilution of quartz evaporates and carbonate minerals variations in sn concentrations probably depend on relative contents of some heavy minerals high sr ba low th u k cs ratios of the saline lake deposits suggest differences in aqueous chemistry of these elements the occurrence of the m type tetrad effect a ree pattern with four convex curves of ree compositions found mainly in the river deposits is considered the result of water particle interaction during chemical weathering of crustal materials y ho ratios of these samples are significantly higher than those of chondrite and the ucc this suggests different chemical behavior of these two elements and possibly the enrichment of carbonate materials the low lree hree feature of the saline lake deposits can be interpreted as due to the different aqueous chemical behavior of the ree s however it can also be reasonably considered as the result of inheritance from their provenance since lree and lree hree variations may be related to the geological setting of the source according to some elements that are not significantly fractionated the average provenance composition of these quaternary deposits are probably characterized by enrichments of ni cr and v over fe higher la th lower la sc and th sc and lower ta w and nb w ratios compared with the ucc composition

geochronology geochemistry and sr nd isotopes of the granitic rocks associated with tungsten deposits in beishan district nw china central asian orogenic belt petrogenesis metallogenic and tectonic implications abstract the beishan orogenic belt is an important tectonic unit and a suitable target to investigate and understand the paleozoic tectonic framework of the central asian orogenic belt paleozoic granitic rocks are widely distributed in the area and closely related to the tungsten deposits at hongjianbingshan guoqing yingzuihongshan and yushan to understand the petrogenesis of the intrusions we performed sims zircon u pb o and whole rock major trace element contents and sr nd isotopic analyses two major suites of granitic intrusions associated with tungsten mineralization have been recognized during 424 314 ma and 286 244 ma the former suite shows variable sr nd and o compositions average 87sr 86sr i 0 7149 or 0 7034 end t 6 3 or 7 6 t2dm 1 68 or 0 41 ga 18o 9 3 or 5 9 indicating an ancient crust or a juvenile lower crust origin whereas the latter suite shows a type affinity and the sr nd and o compositions average 87sr 86sr i 0 7125 end t 4 5 t2dm 1 42 ga 18o 6 9 suggest the precambrian metasedimentary strata may have exerted a significant role in the magma source the proposed magma sources combined with the geochemical differences between these two suites of intrusions indicating the silurian carboniferous mineralization such as hongjianbingshan guoqing and yingzuihongshan are closely associated with subduction accretion and generation of gongpoquan arc accretionary system while the permian mineralization including yushan deposit are attributed to continuing accretion and subsequent post collision these tungsten related granitic rocks are enriched in lree and depleted in hree and ba sr nb p eu and ti suggesting they may have experienced advanced fractional crystallization furthermore a spectacular tetrad effect in their ree distribution patterns has been discovered showing the granites are highly evolved rocks with strong hydrothermal interaction the prolonged fractional crystallization and magmatic hydrothermal interactions have contributed to the formation of the silurian permian tungsten mineralization

timing of lake level changes in etosha pan namibia since the middle holocene from osl ages of relict shorelines in the okondeka region abstract in 2003 examination of aerial photographs revealed a series of previously unknown relict shorelines on the arcuate ridge possibly a clay lunette dune that marks the western boundary of etosha pan in namibia the shorelines are 120 600 m wide and the most prominent extend for tens of km around the lunette dune the shorelines were examined on the ground in 2004 and an attempt was made to date the three lowest levels at ca 5 2 5 and 1 m above the present pan surface the osl ages obtained indicate higher and more prolonged lake conditions than today at ca 6 4 4 0 and 2 1 ka with the youngest shoreline sediments resting on an ancient pan surface dating to ca 13 ka the evidence indicates dry conditions in the pan at ca 13 ka wetter conditions and higher lake levels in the middle holocene followed by a decline in lake levels to the present periods of inundation were of sufficient duration to produce shorelines at the southwestern end of the pan due to the prevailing northeasterly winds that would have maximized wave action along this section of the pan margin the etosha findings together with other regional paleoclimate data suggest four periods of increased wetness in sw africa during the holocene at 7 5 4 5 3 5 2 5 1 7 and ca 1 0 ka there is widespread evidence for the oldest of these periods suggesting that it was a prominent and widespread interval of wetness prior to ca 8 0 ka the climate may have been drier than today

the formation of nuggets of highly siderophile elements in quenched silicate melts at high temperatures before or during the silicate quench the highly siderophile elements hse are powerful tracers of planetary differentiation despite the importance of their partitioning between silicate and metal for the understanding of planetary core formation especially for the earth and mars there is still a huge discrepancy between conclusions based on different high temperature ht experimental studies these disagreements may be due to the presence of hse micro and nanonuggets in ht experiments the formation of these nuggets is still interpreted in different ways one hypothesis is that these hse nuggets formed during the quench of the silicate melt while another hypothesis supposes that these nuggets formed before the quench and represented artefacts of ht experiments the goal of this work is to clarify whether the presence of hse nuggets in silicate melts is linked to a quench effect or not understanding the formation of these hse nuggets represents thus a necessary step towards the resolution of the earth s core formation scenarios we performed new ht experiments 1275 2000 c at different oxygen fugacities fo 2 between ambient air up to 5 log units below the iron wustite buffer iw 5 for two different silicate compositions synthetic martian and terrestrial basalts mixed with a metallic mixture of pt au pd ru our 1275 1600 c experiments were contained in either olivine diopside or graphite crucible experiments at 2000 c were performed using a levitation method so no capsule was necessary our samples contained quenched silicate melts minerals olivine pyroxene spinel depending on the run a two phase metallic bead and nano and micro nuggets of hse our samples underwent fine textural structural and analytical characterizations the distribution of the nuggets was not homogeneous throughout the quenched silicate melt hse nuggets were present within crystals dendritic textures from the quenched silicate melt formed around hse nuggets which could be crystallized showing that the nuggets acted as nucleation sites during the quench thus they predated the quench finally these nuggets also had strong heterogeneities suggesting at least a two stage formation process under reducing conditions consequently our observations clearly show that these hse nuggets formed before the quench in the silicate melt our results agreed with previous studies which concluded that hse abundances in the earth s mantle require the late accretion of chondritic material subsequent to core formation however the effects of metallic si o h or the effect of pressure on the hse partitioning are still not fully understood further work to constrain these effects is to be encouraged to understand the earth s core formation

holocene and deglacial ocean temperature variability in the benguela upwelling region implications for low latitude atmospheric circulation 1 mg ca analyses of g bulloides and abundances of n pachyderma left coiling from ocean drilling program odp leg 175 hole 1084b in the benguela coastal upwelling system document lower sea surface temperatures during the last glacial maximum lgm younger dryas mid holocene and little ice age in the southeastern atlantic taking into consideration the possible effects of differential carbonate dissolution the mg ca data indicate younger dryas temperatures 2 3 c cooler than those of the early holocene and lgm temperatures 4 5 c cooler than those of the early holocene the cool interval during the deglacial period at hole 1084b matches the timing of younger dryas shifts in cariaco basin and greenland ice sheet records and that of a nearby alkenone record comparison of mid holocene cooling at hole odp1084b with other high resolution records of holocene and last deglacial sea surface temperatures from the tropical atlantic implies consistent basin wide changes in atmospheric circulation a brief period of 1 5 2 c cooling between 17 8 and 17 2 ka if related to heinrich event 1 is consistent with a previously hypothesized tropical origin of all heinrich climate change events

genetic significance of the trace element content in metamorphic and hydrothermal quartz a reconnaissance study abstract a reconnaissance study on trace elements in metamorphic and hydrothermal quartz was carried out using quartz samples from the tin district erzgebirge germany the gold mineralization at kasperske hory czech republic and the gold quartz vein deposits muruntau and myutenbai uzbekistan a new method of sample preparation has been developed to prepare pure quartz samples by combining conventional hand picking with microscopic and spectroscopic studies as well as acid wash etch procedures preparation of monomineralic samples was followed by sample dissolution and measurement by icp ms the metamorphic quartz has very low concentrations of li 0 4 ppm al 30 ppm k 35 ppm rb 50 ppb sr 0 3 ppm and y 15 ppb moreover it is characterized by light rare earth element enriched lanthanide distribution patterns lacking eu anomalies the low element concentrations in metamorphic quartz are interpreted to result from recrystallization metamorphic quartz from alteration halos enveloping tin and gold deposits has distinctly different trace element signatures these differences are related to the hydrothermal overprint of the pre existing metamorphic quartz by the mineralizing fluids hydrothermally altered metamorphic quartz from tin deposits has elevated concentrations of li 0 9 ppm al 50 ppm k 45 ppm rb 250 ppb and y 40 ppb whereas altered metamorphic quartz from gold deposits is characterized by elevated concentrations of sr 0 5 ppm the rare earth element distribution patterns of altered metamorphic quartz show variable enrichments of the heavy rare earth elements and frequently display positive eu anomalies hydrothermal vein quartz from the gold deposits usually has elevated al 50 ppm and sr 0 6 ppm contents the lanthanide distribution patterns exhibit variable enrichments of the heavy rare earth elements and commonly show positive eu anomalies the elevated sr concentrations in the quartz from gold deposits are best explained by sr release during feldspar alteration in the wall rocks this mechanism may also account for the relative enrichment of eu in the mineralizing fluids although other processes may not be unambiguously ruled out

rare earth element geochemistry and the tetrad effect abstract the tetrad effect is found in the rare earth elements la lu and results from increased stability at quarter half three quarter and complete filling of the 4f electron shell suggestions that this effect is observed in ree patterns of seawater and other geological samples marine phases the mineral kimuraite late stage granitic rocks the mineral uraninite and siliciclastic sediments are not compelling in the cases of seawater and the carbonate mineral kimuraite a discontinuity at gd may be attributed to the tetrad effect but the complexity of the overall controls on these ree distributions leaves such an interpretation uncertain at best unusual ree patterns in leucogranites and pegmatites are best explained by fractionation of trace minerals notably apatite apparent tetrad anomalies in uraninite rees disappear when normalised to upper crustal i e shale abundances analytical difficulties probably explain apparent tetrad effects in some seawater limestone and siliciclastic ree patterns

metal silicate partitioning of tungsten at high pressure and temperature implications for equilibrium core formation in earth abstract tungsten partitioning between liquid metal and liquid silicate d w from 1723 2673 k 0 5 18 gpa and over a wide range of metal and silicate compositions provides constraints on planetary core formation models we find that w partitioning is extremely sensitive to the carbon content of the metal alloy becoming about an order of magnitude more siderophile at carbon saturation activity composition corrections based on interactions between w c and fe c in metal solution shift calculated d w to more lithophile values and calculated oxygen fugacities fo2 to more oxidizing values than uncorrected data w exists as a highly charged cation in silicate solution displaying a mixture of oxidation states from 4 to 6 in experiments at fo2 of 0 5 2 log units below the iron wustite buffer at constant fo2 the average calculated valence decreases with pressure from 5 5 at 0 5 gpa to 4 at 11 18 gpa as a result of its high oxidation state w partitioning is strongly dependent on silicate melt polymerization and fo2 in contrast to some previous results we find that d w may decrease slightly in response to increasing temperature in the pressure range of our experiments pressure exerts a non monotonic effect d w increases with pressure up to 3 to 4 gpa but decreases at higher pressures previous models for the effects of pressure and temperature on w partitioning that conflict with our results appear to result from a conflation of the intensive parameters of pressure temperature and carbon content the mantle abundance of w could have been set by single stage metal silicate equilibration along the liquidus in a deep peridotite magma ocean at pressures from 20 50 gpa and at oxygen fugacities consistent with the mantle s present iron budget iw 2 to 2 5 equilibration at higher pressure is viable if the core forming metal contained a significant but not unreasonable abundance of carbon 2 wt recent continuous accretion models involving multi stage metal silicate equilibration in a deepening magma ocean with progressive oxidation of the silicate remain permissible given our new treatment of w partitioning data